tag:theconversation.com,2011:/us/topics/west-nile-virus-3632/articlesWest Nile virus – The Conversation2024-03-19T12:23:24Ztag:theconversation.com,2011:article/2237062024-03-19T12:23:24Z2024-03-19T12:23:24ZFemale mosquitoes rely on one another to choose the best breeding sites − and with the arrival of spring, they’re already on the hunt<figure><img src="https://images.theconversation.com/files/582309/original/file-20240315-26-7bf0sq.jpg?ixlib=rb-1.1.0&rect=30%2C0%2C6789%2C4468&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">_Aedes aegypti_, found across much of the U.S., spread Zika, dengue, chikungunya and other viruses.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/aedes-aegypti-mosquito-pernilongo-with-white-spots-royalty-free-image/1282216815">Mailson Pignata/iStock via Getty Images</a></span></figcaption></figure><p><em>Aedes aegypti</em> mosquitoes, one of the <a href="https://www.cdc.gov/mosquitoes/mosquito-control/professionals/range.html">most common species in the U.S.</a>, love everything about humans. They love our <a href="http://dx.doi.org/10.1126/science.adi8213">body heat and odors</a>, which enable them to find us. They love to feed on our blood to make their eggs mature. They even love all the standing water that we create. Uncovered containers, old tires and junk piles collect water and are perfect for breeding. </p>
<p>And with the advent of warm weather across the southern U.S., <a href="https://www.mosquitomagnet.com/articles/mosquito-season">mosquito breeding season is already underway</a>.</p>
<p>Given all the options that <em>Aedes</em> females have in urban areas, how do these cosmopolitan mosquitoes find the perfect site to lay their eggs? Scientists previously thought this was a solitary act, but now research shows that female <em>Aedes aegypti</em> mosquitoes – the main vector in the U.S. for diseases such as <a href="https://theconversation.com/explainer-where-did-zika-virus-come-from-and-why-is-it-a-problem-in-brazil-53425">Zika, dengue, chikungunya</a> and other viruses – can rely on one another for good reviews of breeding sites. </p>
<p>Our <a href="https://www.degennarolab.org/">Laboratory of Tropical Genetics</a> at Florida International University discovered a new behavior in which these mosquitoes <a href="https://doi.org/10.1038/s42003-024-05830-5">work together to find suitable egg-laying sites</a>. These findings, recently published in Communications Biology, show that mosquitoes regulate their own population density at breeding sites – an insight that could inform future mosquito control efforts.</p>
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<a href="https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A half-dozen mosquitoes spread along the inside of a container." src="https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581972/original/file-20240314-30-jxgzpm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption"><em>Aedes aegypti</em> female mosquitoes laying their eggs in a laboratory breeding container.</span>
<span class="attribution"><span class="source">Kaylee Marrero</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Where and why female mosquitoes cluster</h2>
<p>Scientists know that female mosquitoes can be picky when it comes to where they lay their eggs. <em>Aedes aegypti</em> look for human-made breeding sites with relatively clean water, such as birdbaths, tires or even water-filled trash. But given two equal choices, you might expect them to spread evenly between the two. </p>
<p>On the contrary, when we released females in a two-choice test where both breeding site options were equivalent, we repeatedly found more mosquitoes in one chamber than in the other. Furthermore, this occurred irrespective of where the preferred chamber was positioned, whether the mosquitoes could touch water or whether mosquito eggs were already present at the breeding sites. </p>
<p>Female mosquitoes clearly were following one another in small groups to one breeding site rather than another – a newly discovered behavior in <em>Aedes aegypti</em> that we call aggregation. </p>
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<a href="https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two ramekins, one with a few black spots in it, the other with many spots." src="https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581971/original/file-20240314-26-70qvqk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The black spots in the container on the right indicate that <em>Aedes aegypti</em> females have chosen it as a place to lay their eggs over the identical site on the left.</span>
<span class="attribution"><span class="source">Kaylee Marrero</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>The insects evidently preferred not to lay their eggs alone. When we tested 30 mosquitoes in our trials, they chose one site over another by a 2-to-1 margin. However, this changed as the test population increased beyond 30 mosquitoes. When we tested 60 or 90 females, the aggregation disappeared.</p>
<p>This tells us that females can regulate their own density at breeding sites – a response that likely is a mechanism to limit larval competition.</p>
<h2>Mosquitoes are smelling each other</h2>
<p>Mosquitoes largely sense the world through smell, using three families of <a href="https://www.britannica.com/science/olfactory-receptor">olfactory receptors</a>. These receptors detect odors when females are choosing where to lay eggs. But how do females sense each other to regulate their densities at breeding sites? </p>
<p>We explored this question by first placing 15 mosquitoes at one of our two test breeding sites. Other females seeking a place to lay preferred the unoccupied site over the one that was already occupied, even though we had already observed that the mosquitoes preferred not to lay their eggs alone. Something was directing them away from the occupied breeding site; we speculated that it might be carbon dioxide, which is an important cue for mosquitoes in all stages of their life cycle. </p>
<p>When female mosquitoes are looking for a blood meal, they fly toward the odor of CO₂, which all vertebrate animals <a href="https://theconversation.com/why-are-some-people-mosquito-magnets-and-others-unbothered-a-medical-entomologist-points-to-metabolism-body-odor-and-mindset-187957">exhale and release through their skin</a>. After feeding, they fly away from it, likely to avoid the risk of being killed by the host. </p>
<p>Mosquitoes also emit CO₂, and normally other mosquitoes can smell it, thanks to a receptor component called Gr3 in their olfactory organs. But when we released mutant females that lacked a functional Gr3 receptor to seek a place to lay eggs in our two-site test, we found that these insects, which could not detect CO₂, were willing to lay their eggs at preoccupied breeding sites. This suggested that normal mosquitoes might be avoiding the preoccupied laying site because they smelled CO₂ emitted by mosquitoes that were already there.</p>
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<figcaption><span class="caption">Female mosquitoes lay eggs on or near still bodies of water.</span></figcaption>
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<p>To confirm this, we offered two unoccupied breeding sites to females seeking a place to lay. However, we increased CO₂ levels around one of the sites to between 600 and 750 parts per million, compared with the normal level of about 450 to 500 ppm at the other site. We found that <em>Aedes aegypti</em> females avoided the unoccupied sites with elevated CO₂. This behavior appears designed to keep occupied breeding sites from becoming too crowded. </p>
<p>Overall, we found that two families of receptors play a role in the interactions between <em>Aedes aegypti</em> females when they seek breeding sites. Odorant receptors detect an unknown odor, which draws females toward a site; gustatory receptors detect CO₂, which deters females from breeding sites when the carbon dioxide level is high. The balance between these attractive and repellent odors will ultimately determine whether a female chooses or avoids a particular site. </p>
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<a href="https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graphic showing common mosquito breeding sites around home, including gutters and pet dishes." src="https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/582583/original/file-20240318-20-i9yyck.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Mosquitoes breed in many wet spots, large and small.</span>
<span class="attribution"><a class="source" href="https://www.cabq.gov/environmentalhealth/urban-biology/mosquitoes">City of Albuquerque</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<h2>Implications for mosquito control</h2>
<p>Suppressing mosquito populations in urban areas using <a href="https://www.cdc.gov/mosquitoes/mosquito-control/community/larvicides.html">biolarvicides</a> – pesticides made from live bacteria that are toxic to mosquito larvae – is a primary control strategy to limit the spread of deadly diseases such as West Nile virus and Zika virus. This is especially true for <em>Aedes aegypti</em>, which is the most common urban mosquito species that reproduces in artificial breeding sites that humans create. Other control tactics, such as <a href="https://undark.org/2019/10/25/when-residents-say-no-to-aerial-mosquito-spraying/">spraying pesticides over large areas</a>, target beneficial insects as well as mosquitoes and can be controversial. </p>
<p>Knowing that female <em>Aedes aegypti</em> use social cues to pick the best breeding grounds for their young and will move on from a breeding site when it becomes too crowded could lead to new control measures. Interrupting the female mosquito reproductive cycle would reduce the spread of mosquitoes and the spread of diseases that these insects carry.</p><img src="https://counter.theconversation.com/content/223706/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kaylee Marrero receives funding from the National Institutes of Health.</span></em></p><p class="fine-print"><em><span>Andre Luis Costa-da-Silva receives funding from the Centers for Disease Control and Prevention, the Southeastern Center of Excellence in Vector-borne Disease and the National Institutes of Health. Views expressed in this article are his own. </span></em></p><p class="fine-print"><em><span>Matthew DeGennaro receives funding from the Centers for Disease Control and Prevention (CDC), the Southeastern Center of Excellence in Vector-borne Disease and the National Institutes of Health. Views expressed in this article are his own.</span></em></p>Female mosquitoes don’t want to lay their eggs alone, but they don’t want sites that are too crowded either. Understanding what guides their choice could inform new control strategies.Kaylee Marrero, Ph.D. Student and Transdisiplinary Biomolecular and Biomedical Sciences Fellow, Florida International UniversityAndre Luis da Costa da Silva, Research Assistant Professor of Biological Sciences, Florida International UniversityMatthew DeGennaro, Associate Professor of Biological Sciences, Florida International UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2129552023-09-17T12:07:36Z2023-09-17T12:07:36ZWhat Canadians need to know about West Nile virus, a mosquito-borne infection that can be life-threatening<iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/what-canadians-need-to-know-about-west-nile-virus-a-mosquito-borne-infection-that-can-be-life-threatening" width="100%" height="400"></iframe>
<p>During the late summer of 1999, New York City recorded an <a href="https://doi.org/10.2105%2Fajph.92.8.1218">unusual number of cases of encephalitis</a> (inflammation of the brain). At the same time, the <a href="https://www.nationalgeographic.com/science/article/west-nile-virus-the-stranger-that-came-to-stay">Bronx Zoo</a> reported a massive death of birds and mammals. </p>
<p>The human encephalitis cases might have been attributed to a flare-up of an endemic arbovirus (<a href="https://ndc.services.cdc.gov/case-definitions/arboviral-diseases-neuroinvasive-and-non-neuroinvasive-2015/">a virus transmitted by a tick or mosquito bite</a>) such as <a href="https://www.cdc.gov/sle/index.html">St. Louis encephalitis</a>, but the concurrent bird and mammal deaths suggested the human illnesses warranted further investigation. </p>
<p>Scientists eventually identified these as the first confirmed cases of West Nile virus (WNV) in North America.</p>
<h2>West Nile virus in North America</h2>
<p>WNV was first reported in a woman with a fever in Uganda in 1937. An <a href="https://doi.org/10.2214/ajr.184.3.01840957">outbreak in Israel in 1957</a> established WNV as a cause of <a href="https://doi.org/10.3201/eid0704.017416">severe meningoencephalitis</a> (inflammation of the spinal cord and brain) in elderly patients. </p>
<p>Several clusters or medium-range outbreaks were reported from Asia, Europe and Africa in the 20th century. Finally, the virus managed to cross the Atlantic and landed in North America in 1999.</p>
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<img alt="Round blue particles nestled in a red matrix" src="https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=570&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=570&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548213/original/file-20230914-19-x6rm98.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=570&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Microscopic view of West Nile virus particles in a cell.</span>
<span class="attribution"><span class="source">(NIAID)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>In 1999, the <a href="https://www.cdc.gov/westnile/statsmaps/historic-data.html">case number</a> was limited to 62 in New York City, and there was concern about a huge surge in 2000. Fortunately, the case number in 2000 was 21, which is exceedingly low, but it had spread to New Jersey and Connecticut. The case number remained in a similar low range (only 66 cases) in 2001. </p>
<p>However, the virus hit hard the following year. In 2002, the case number rose to over 4,000 in the United States. The same year, <a href="https://www.canada.ca/en/public-health/services/diseases/west-nile-virus/surveillance-west-nile-virus.html">Canada experienced its first cases</a> in Ontario.</p>
<p>The U.S. has reported a <a href="https://www.cdc.gov/westnile/statsmaps/historic-data.html">cumulative total</a> of 56,569 cases and 2,773 deaths, while <a href="https://www.canada.ca/en/public-health/services/diseases/west-nile-virus/surveillance-west-nile-virus.html#a1">Canada has reported 6,683 cases</a> and about 150 deaths (I’m told by the Centre for Food-borne, Environmental & Zoonotic Infectious Diseases, Public Health Agency of Canada), with the highest number of cases observed in the U.S. in 2003 and in Canada in 2007.</p>
<p>This virus spread across the entire continent very quickly, and covered most of North America by 2005. However, it took almost 10 years for the virus to <a href="https://doi.org/10.1089/vbz.2010.0062">show up in British Columbia</a>. In Canada, most of the cases were found in the Prairie region (Alberta, Saskatchewan and Manitoba). <a href="https://www.cdc.gov/westnile/statsmaps/historic-data.html">In the U.S.</a>, Midwestern states have been most affected.</p>
<p>West Nile virus is an RNA virus, a close cousin of <a href="https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue">Dengue</a>, <a href="http://www.bccdc.ca/health-info/diseases-conditions/yellow-fever">Yellow fever</a>, St. Louis encephalitis and <a href="http://www.bccdc.ca/health-info/diseases-conditions/zika-virus">Zika virus</a>, to name a few. It belongs to the family Flaviviridae. </p>
<h2>Symptoms and transmission</h2>
<p><a href="https://www.cdc.gov/westnile/symptoms/index.html">Approximately 80 per cent of people</a> exposed to WNV are asymptomatic. <a href="https://doi.org/10.14745/ccdr.v40i10a01">The incubation period</a> in humans is about a week; however, this ranges from two to 15 days after the virus enters the body.</p>
<p>Among symptomatic individuals, all of them experience fever, and many also experience headaches, body aches, a mild rash and swollen lymph glands to varying degrees. </p>
<p>Although most cases go unnoticed, the virus still has deadly potential. <a href="https://nccid.ca/debrief/west-nile-virus/">A small number of people</a> (around one per cent) experience severe symptoms, including encephalitis. However, over the years, the <a href="https://doi.org/10.1038/ncpneuro0176">number of neurological cases has been increasing</a>.</p>
<p>This virus is mostly <a href="https://www.who.int/news-room/fact-sheets/detail/west-nile-virus">transmitted via mosquito bites</a>; however, very rarely it could transmit via blood transfusion, organ or tissue transplants, from mother to unborn babies and through exposure to infected animals. </p>
<p>A number of birds, predominantly corvids such as crows, jays and magpies, act as reservoirs as well as <a href="https://www.biologyonline.com/dictionary/amplifier-host">amplifying hosts</a>. When an uninfected mosquito feeds on an infected bird and then bites a healthy human, the human becomes infected. </p>
<p>Humans are considered dead-end hosts, meaning that even if a mosquito feeds on an infected individual, that mosquito cannot transmit the virus to another individual <a href="https://www.who.int/news-room/questions-and-answers/item/dengue-and-severe-dengue">as can happen with the dengue virus</a>.</p>
<p>Once people are severely infected with West Nile virus, they <a href="https://www.cdc.gov/westnile/symptoms/index.html">acquire longer immunity</a>. Older people are usually at high risk for severe infection due to underlying health conditions. People with diabetes and uncontrolled hypertension <a href="https://www.canada.ca/en/public-health/services/diseases/west-nile-virus/risks-west-nile-virus.html">have a greater risk</a> of developing severe neurological disease from the West Nile virus. </p>
<h2>Diagnosis</h2>
<p>Patients who become ill with a fever and severe headache within a few days of a mosquito bite should visit their family physician or any health-care facility.</p>
<p>Because WNV is closely related to other pathogens, diagnosis is often challenging.
Patient signs and symptoms, history of mosquito bites and laboratory tests are all important when assessing patients for possible infection with West Nile virus.</p>
<p>The most common <a href="https://www.publichealthontario.ca/en/Laboratory-Services/Test-Information-Index/West-Nile-Virus-Serology">laboratory test</a> is to detect antibodies against WNV in the blood. However, WNV antibodies cross-react with dengue, Zika or other flaviviruses, so if this test is positive, an additional test is required to confirm the diagnosis. </p>
<p>This additional test is called the Plaque Reduction Neutralization Test or PRNT for short. It requires a live virus, so it must be done in a containment level 3 (CL3) laboratory. </p>
<p>The laboratory can also diagnose viral RNA using molecular tests, but interestingly, the virus often disappears from the blood when people exhibit symptoms. For encephalitic patients, cerebrospinal fluid can be used to detect the virus using molecular methods such as a polymerase chain reaction (PCR) test.</p>
<h2>Preventive measures</h2>
<p>There is no human vaccine for the West Nile virus. The most important preventive measure to avoid West Nile virus infection is to avoid mosquito bites. This seems simple but is often very challenging. </p>
<figure class="align-center ">
<img alt="Close-up view of a mosquito held with tweezers" src="https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548224/original/file-20230914-17-vsdb54.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A Culex tarsalis mosquito, a species that can transmit West Nile virus to humans, and is found across Canada.</span>
<span class="attribution"><span class="source">(AP Photo/Rick Bowmer)</span></span>
</figcaption>
</figure>
<p>People should use common sense during outdoor and indoor activities. Mosquito bites can be prevented by using bug spray, wearing protective clothing and avoiding areas that may have mosquitoes during the times when the species is most active, typically dusk and dawn. </p>
<p>A few species of mosquitoes can transmit WNV to humans. Among these, two of the most common species — the Culex pipiens and Culex tarsalis — are found across Canada, and their habitat is <a href="https://ncceh.ca/resources/evidence-reviews/impacts-canadas-changing-climate-west-nile-virus-vectors">predicted to expand with climate change</a>. Mosquitoes not only transmit WNV, but also transmit <a href="https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/california-serogroup-pathogen-safety-data-sheet.html">California serogroup viruses</a>, which cause encephalitis, as well as <a href="https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/eastern-equine-encephalitis.html">eastern equine encephalitis</a> viruses. </p>
<p>There is also no specific treatment for West Nile virus; medical management is supportive. Patients with severe symptoms often require pain control for headaches and medication and rehydration to treat nausea and vomiting. </p>
<p><a href="https://www.canada.ca/en/public-health/services/diseases/west-nile-virus/surveillance-west-nile-virus/west-nile-virus-weekly-surveillance-monitoring.html">So far in 2023</a>, only a <a href="https://www.cbc.ca/news/canada/hamilton/hamilton-west-nile-virus-2023-1.6957260">few human cases</a> have been identified in Ontario. However, a few mosquito pools in Manitoba and Ontario also tested positive, and also a few WNV-positive birds were found in Saskatchewan, Manitoba, Ontario and Québec.</p>
<p>No matter how many cases we are seeing, everyone is advised to take precautions against mosquito bites to avoid these life-threatening diseases.</p><img src="https://counter.theconversation.com/content/212955/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Muhammad Morshed does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>West Nile virus arrived in North America in 1999 and spread across the continent by 2005. Here’s what you need to know about this mosquito-borne pathogen.Muhammad Morshed, Clinical Professor, Department of Pathology and Laboratory Medicine, University of British ColumbiaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1844122022-09-09T12:34:01Z2022-09-09T12:34:01ZLa Crosse virus is the second-most common virus in the US spread by mosquitoes – and can cause severe neurological damage in rare cases<figure><img src="https://images.theconversation.com/files/481864/original/file-20220830-19040-p60irc.jpg?ixlib=rb-1.1.0&rect=22%2C45%2C4998%2C3229&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">People catch La Crosse disease primarily from the bite of the eastern tree-hole mosquito – although two other species may also carry the virus.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/mosquito-sucking-blood-on-human-skin-royalty-free-image/1218518415?adppopup=true">Nipol Plobmuang/EyeEm via Getty Images</a></span></figcaption></figure><p>For the Laudick family of Greensburg, Indiana, life forever changed on Aug. 5, 2013. That was the day 4-year-old Leah Laudick told her mom, Shelly, that she had a bad headache. </p>
<p>Two days later, Leah was hospitalized nearby with worsening headaches and a slightly elevated white blood cell count. She slept for most of the day and by Aug. 9 was largely unresponsive. </p>
<p>That day, during her transfer to Peyton Manning Children’s Hospital in Indianapolis, Leah had her first of several seizures. Doctors were unable to identify her illness – tests for diseases like meningitis, Rocky Mountain spotted fever and herpes simplex all came back negative. </p>
<p>One day later, on Aug. 10, Leah’s brain activity stopped. That evening she passed away in the arms of her grieving parents. </p>
<p>A few months later, the Laudicks learned from the Centers for Disease Control and Prevention that an illness called La Crosse disease, contracted from the bite of a mosquito, had caused Leah’s death. </p>
<p>I am <a href="https://epp.tennessee.edu/directory/dr-rebecca-trout-fryxell/">an entomologist</a> at the University of Tennessee who studies how La Crosse disease spreads in the environment. I met the Laudicks – they have given me permission to tell their story – when Leah’s father, Andy, emailed me asking how he could help with my work. Such emails from parents of La Crosse-infected children are why I continue to study the virus. </p>
<p>Together with other <a href="https://www.mdpi.com/2075-4450/13/2/164">researchers at the University of Tennessee</a> and Western Carolina University, I’m working to provide people and communities with effective solutions to preventing this illness. Through my research and <a href="https://www.megabitess.org/">community engagement activities</a>, I am helping to increase awareness of what La Crosse virus is and how people catch it – and can avoid catching it. </p>
<h2>What is La Crosse disease?</h2>
<p><a href="https://www.cdc.gov/lac/index.html">La Crosse disease</a> is the nation’s <a href="https://doi.org/10.15585%2Fmmwr.mm7032a1">second-most prevalent mosquito-borne virus</a>. According to the CDC, West Nile virus makes up <a href="https://www.cdc.gov/mmwr/volumes/68/wr/mm6831a1.htm">more than 90% of annual viral infections</a> from mosquito or tick bites, with <a href="https://www.cdc.gov/mmwr/volumes/68/wr/mm6831a1.htm">La Crosse the next-most prevalent</a> at about 2% of mosquito or tickborne viral infections a year – <a href="https://www.cdc.gov/lac/statistics/index.html">or 50 to 150 cases a year</a>. Both children and adults can be infected with La Crosse virus.</p>
<p>La Crosse was first identified in the U.S. in 1960, and historically, most cases have occurred in <a href="https://doi.org/10.1371/journal.pone.0006145">Upper Midwest</a> and Mid-Atlantic states. Leah’s case was the only one reported in Indiana in 2013. </p>
<p>The majority now occur in the southern Appalachia region, which stretches from northern Alabama and Georgia, across eastern Tennessee and western North Carolina, and north to parts of Kentucky, Virginia and West Virginia. We still do not know why this is the case, but there are <a href="https://doi.org/10.1007/s10393-012-0773-7">many hypotheses</a> centered around climate, land use and invasive mosquito species.</p>
<p><iframe id="2m3d9" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/2m3d9/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>How do people catch La Crosse?</h2>
<p>La Crosse virus is carried and transmitted primarily <a href="https://wrbu.si.edu/vectorspecies/mosquitoes/triseriatus">by the eastern tree-hole mosquito</a>, <em>Aedes triseriatus</em>, a native species found throughout most of the Eastern U.S. This mosquito’s preferred habitat is places with obvious tree holes <a href="https://wrbu.si.edu/vectorspecies/mosquitoes/triseriatus">for female mosquitoes to deposit their eggs</a>, such as hardwood forests.</p>
<p>However, the virus <a href="https://doi.org/10.2987/moco-31-03-233-241.1">may also be transmitted</a> – although not as well – by two exotic and invasive mosquito species: the <a href="https://www.wrbu.si.edu/vectorspecies/mosquitoes/albopictus">tiger mosquito</a>, <em>Aedes albopictus,</em> and <a href="https://www.wrbu.si.edu/index.php/vectorspecies/mosquitoes/japonicus">the bush mosquito</a>, <em>Aedes japonicus.</em></p>
<p>Tiger and bush mosquitoes are spreading throughout the U.S. in response to changes in landscape and climate, and also by hitchhiking inside water-filled containers. Our team has <a href="https://doi.org/10.1371/journal.pone.0237322">found them</a> together in the same habitats as eastern tree-hole mosquitoes, in places with hardwood trees like parks, cemeteries and residential backyards. Our team has also found these mosquitoes in <a href="https://doi.org/10.1371/journal.pone.0237322">close proximity</a> to confirmed La Crosse cases.</p>
<p>All three mosquito species develop in the same water sources and feed on mammals, including humans. Some <a href="https://doi.org/10.1007/s10393-012-0773-7">scientists speculate that</a> these factors have been key to the distribution of La Crosse in the Appalachian region, although there is still a lot to learn about these mosquito species and their role in spreading the virus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close-up photo of the eastern treehole mosquito." src="https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/483611/original/file-20220908-9281-7nbj62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The eastern tree-hole mosquito is the primary carrier of La Crosse virus.</span>
<span class="attribution"><span class="source">Dave Paulsen, Department of Entomology and Plant Pathology, University of Tennessee</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Diagnosing La Crosse is difficult</h2>
<p>La Crosse disease is easy to misdiagnose, in part because its symptoms can be easily confused with those of other illnesses, such as the flu. Moreover, the only way to test for La Crosse involves <a href="https://www.cdc.gov/lac/healthcare-providers/diagnostic-testing.html">sending samples of blood and cerebrospinal fluid</a> to the CDC.</p>
<p>However, La Crosse infections <a href="https://doi.org/10.1371/journal.pone.0006954">tend to cluster in local communities</a> from year to year. For example, of the 115 cases reported in Tennessee since 2011, <a href="https://www.tn.gov/health/cedep/vector-borne-diseases/mosquito-borne-diseases/mosquito-borne-diseases-of-concern/la-crosse-encephalitis.html">most occurred in less than 20%</a> of the state’s 95 counties. So even a few successfully diagnosed cases can tip off local doctors and officials that the disease is present in their area. </p>
<h2>Symptoms of La Crosse</h2>
<p>Symptomatic cases of La Crosse begin with a mild illness involving fever, fatigue, vomiting and headache. This lasts for nearly two weeks. Most infected individuals recover fully.</p>
<p>However, like West Nile, La Crosse disease is “neuroinvasive,” meaning it can invade and affect the central nervous system.</p>
<p><a href="https://doi.org/10.1186/s12974-021-02173-4">Research suggests that age</a>, the <a href="https://doi.org/10.1186/s12974-017-0836-3">development of the immune system</a> and the <a href="https://doi.org/10.3201%2Feid2105.141992">strain of the virus</a> are key factors in whether someone develops neuroinvasive La Crosse, while delays in seeking medical help <a href="https://doi.org/10.1056/NEJM200103153441103">also influence its severity</a>. The most susceptible are immunocompromised individuals and children – more than 60 children a year are diagnosed with neuroinvasive La Crosse. </p>
<p>Severe cases <a href="https://doi.org/10.1542/hpeds.2012-0022">are usually discovered in the hospital</a> after the patient experiences a seizure, coma, partial paralysis of one side or altered mental state. </p>
<p>Severe La Crosse can result in <a href="https://doi.org/10.1093/cid/ciac403">long-term neurological damage</a>. Deaths caused by infection are rare, but neurological and behavioral effects can occur after infection, including cognitive disorders, diagnoses of attention-deficit/hyperactivity disorder and <a href="https://doi.org/10.1212/WNL.18.10.1023">reduced IQ scores</a>.</p>
<h2>Can La Crosse disease be prevented?</h2>
<p>Until the scientific community understands more about the ecology and epidemiology of La Crosse, my colleagues and I will continue to recommend preventing the mosquito bite in the first place to avoid infections.</p>
<p>One tactic is to reduce local opportunities for the mosquitoes that carry La Crosse to breed. This includes getting rid of objects outdoors that can catch and contain water – like empty plant pots, cans or toys – because these <a href="https://doi.org/10.52707/1081-1710-46.1.34">can emulate the conditions of a mosquito-friendly forest</a>. Mosquitoes carrying La Crosse virus are also found developing in tires containing water, so it’s a good idea <a href="https://doi.org/10.1093/jmedent/35.4.573">to drill drainage holes in tire swings</a>.</p>
<figure class="align-center ">
<img alt="Researcher crouching near the ground at sunny spot within a forest." src="https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/483330/original/file-20220907-9232-jgyaex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Rebecca Trout Fryxell looks for mosquitoes in a puddle created by an above-ground tree root.</span>
<span class="attribution"><span class="source">Trout Fryxell’s Medical and Veterinary Entomology Laboratory, Univ. of Tennessee</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Another strategy is to try to avoid mosquitoes, perhaps by staying inside during peak mosquito hours, which are typically in the <a href="https://doi.org/10.2987/16-6620R.1">early evening</a>.</p>
<p>Using area repellents such as mosquito coils, wearing light-colored clothing and applying mosquito repellent can also help prevent bites. </p>
<p>The Environmental Protection Agency’s <a href="https://www.epa.gov/insect-repellents/find-repellent-right-you">guide to the active ingredients in insect repellents</a> describes which are most effective at repelling mosquitoes and how many hours they last. Like sunscreen, insect repellents may need to be reapplied while spending time outdoors. </p>
<p>Leah Laudick adored her six siblings and “enjoyed collecting rocks, chasing butterflies and picking flowers for her mom,” in the words of her father. </p>
<p>As officials and the public learn more about La Crosse, both avoiding and diagnosing the infection could become easier, and more lives like Leah’s could be saved.</p><img src="https://counter.theconversation.com/content/184412/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rebecca Trout Fryxell receives funding from the United States Department of Agriculture. </span></em></p>Not all cases of La Crosse disease affect the neurological system, but those that do can be severe and sometimes fatal – especially in children.Rebecca Trout Fryxell, Associate Professor of Medical and Veterinary Entomology, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1888562022-08-18T14:11:44Z2022-08-18T14:11:44ZMosquitoes: there’s malaria, plus 5 other diseases they pass on to humans<figure><img src="https://images.theconversation.com/files/479588/original/file-20220817-16-p6zz3e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Tacio Philip Sansonovski/Shutterstock</span></span></figcaption></figure><p>Most people instantly associate mosquitoes with malaria. But these tiny flying insects can transmit a number of <a href="https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases">other diseases</a> too. </p>
<p>Viruses transmitted by insects like mosquitoes are called arthropod-borne or arboviruses. Like malaria, these viruses are transmitted to vertebrate hosts through the <a href="https://www.medicalnewstoday.com/articles/311485">bite of a female mosquito</a> when she takes a blood meal to assist with her egg development. Most vertebrate hosts for these arboviruses are non-human. They include birds, primates and agricultural animals. But some arboviruses can be transmitted to humans with severe negative outcomes. </p>
<p>Five of the most important arboviruses affecting communities in Africa include the chikungunya, dengue, West Nile, yellow fever and Zika viruses. It is <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8055094/">estimated</a> that half of the world’s population is at risk of being infected by an arbovirus.</p>
<p>Some mosquito-borne diseases – but not all – can be fatal to humans. This confirms that every effort must be made to prevent being bitten by a mosquito and infected using both pharmaceutical and non-pharmaceutical measures.</p>
<h2>Chikungunya</h2>
<p>The name chikungunya is derived from the Kimakonde language (used in Tanzania and Mozambique) and means “<a href="https://www.worldmosquitoprogram.org/sites/default/files/2022-04/WMP%20chikungunya%20%281%29.pdf">to become contorted</a>”. The symptoms of chikungunya virus include headaches, a rash, fatigue, fever and muscle and joint pain. Generally these symptoms clear within a week. Occasionally, an infection can result in a severe fever and extremely painful joints, which can last for months or years, inducing a hunched, contorted appearance. Unfortunately, there are no antiviral or vaccine treatments available for chikungunya virus. Deaths from chikungunya are rare and are generally associated with other underlying health problems.</p>
<p>The chikungunya virus was first identified in <a href="https://www.worldmosquitoprogram.org/en/learn/mosquito-borne-diseases/chikungunya">1952</a> during an outbreak in Tanzania. It is transmitted by <em>Aedes aegypti</em> and <em>Aedes albopictus</em> mosquitoes. Over 100 countries across the globe have reported chikungunya virus cases. The risk of outbreaks is extremely high wherever these mosquito species are present around homes and urban areas.</p>
<p>Female <em>Aedes</em> mosquitoes tend to feed just after sunrise and around sunset. They lay eggs that can survive drying out. This makes vector control rather challenging. Current control strategies focus on reducing the number of water containers that these mosquitoes like to breed in, the use of insecticides against adult mosquitoes and personal protection to prevent mosquito bites.</p>
<h2>Dengue</h2>
<p>The World Health Organization has classified <a href="https://www.worldmosquitoprogram.org/sites/default/files/2022-04/WMP%20dengue%20%281%29.pdf">dengue virus</a> as one of the top ten global health threats. It’s one of the fastest spreading mosquito-borne diseases. At least half of the world’s population is at risk of infection. </p>
<p>Like chikungunya virus, dengue is spread by <em>Aedes aegypti</em> and <em>Aedes albopictus</em> mosquitoes. Both viruses share the same control interventions and non-specific symptoms of headaches, a rash, fever and muscle and joint pain, so they are often misdiagnosed. </p>
<p>Most human cases of dengue are asymptomatic or present with mild symptoms, which last for two to seven days. In certain individuals, dengue virus progresses to severe disease and symptoms include persistent vomiting, bleeding gums or nose and enlarged liver. This must be treated as a medical emergency as these complications can be lethal. Dengue virus can be diagnosed using a rapid diagnostic test or a polymerase chain reaction (PCR) test. </p>
<p>But there is no treatment available. A vaccine has been developed and has been approved for use in a few countries – but is not widely available in <a href="https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue">Africa at present</a>. </p>
<h2>Zika</h2>
<p>The Zika virus was identified in humans in the 1950s. But it only became a pathogen of major public concern in 2016 following the <a href="https://www.worldmosquitoprogram.org/en/learn/mosquito-borne-diseases/zika">2015 Zika virus pandemic</a>. The virus is transmitted by <em>Aedes aegypti</em> and <em>Aedes albopictus</em> mosquitoes, and is generally non-lethal in humans. Most people infected with Zika virus do not show any symptoms. A few have non-specific symptoms like fever, rash, headaches, muscle and joint pains and conjunctivitis. These can last two to seven days. </p>
<figure class="align-center ">
<img alt="parent and children working out in swimming pool" src="https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/479591/original/file-20220817-15-uou8bk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The 2015 Zika outbreak resulted in scores of babies born with microcephaly.</span>
<span class="attribution"><span class="source">Joa Souza/Shutterstock</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Individuals infected with Zika virus while pregnant are at an <a href="https://www.who.int/news-room/fact-sheets/detail/zika-virus">increased risk</a> of stillbirth, abortion, neurological disorders or delivering children with birth defects, including microcephaly. PCR testing can be used to diagnose Zika virus, but there is no treatment available.</p>
<h2>Yellow fever</h2>
<p><em>Aedes aegypti</em> and <em>Aedes albopictus</em> mosquitoes are also responsible for the transmission of yellow fever, so named because the virus causes jaundice (yellowing of eyes and skin due to impaired liver function).</p>
<p>Symptoms in mild cases <a href="https://www.worldmosquitoprogram.org/en/learn/mosquito-borne-diseases/yellow-fever">include</a> fever, headaches, chills, back pain, fatigue, jaundice, vomiting and bleeding from the mouth, nose, eyes or stomach. These generally clear within five days. Approximately 50% of the small number of patients who develop severe symptoms will die with 10 days of becoming infected. Yellow fever can be diagnosed by PCR or enzyme-linked immunosorbent assay (ELISA). Although there is no treatment for yellow fever, a very effective vaccine is widely available. A single vaccine dose provides <a href="https://www.who.int/news-room/fact-sheets/detail/yellow-fever">lifelong immunity</a>, so all individuals living in or travelling to areas endemic for yellow fever should take the vaccine.</p>
<h2>West Nile</h2>
<p>The West Nile virus was first isolated from a woman in the <a href="https://www.who.int/news-room/fact-sheets/detail/west-nile-virus">West Nile region of Uganda</a>. It is transmitted by mosquitoes belonging the genus <em>Culex</em>. The natural vertebrate hosts are wild birds. But the virus can be transmitted to a number of different animals, including humans, through the bite of an infected mosquito. Approximately 80% of the people infected with West Nile virus will not show any symptoms. Those who do become symptomatic have mild non-specific symptoms that include headaches, fever, tiredness, body aches, nausea, vomiting and, occasionally, a rash. A small proportion of symptomatic patients, however, develop severe disease. This is associated with neurological impairment, and can be fatal in extreme cases. </p>
<p>West Nile virus infection can be diagnosed by PCR or ELISA, with only supportive treatment available for neurological impairment. It has been suggested that people who are older than 50 or immunocompromised are at greater risk of severe infection. An integrated approach comprising water management together with chemical and biological interventions is needed to control the spread of the <em>Culex</em> vectors.</p><img src="https://counter.theconversation.com/content/188856/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jaishree Raman receives funding from the Gates Foundation, the Global Fund, the South African Medical Research Council, the Research Trust, National Research Foundation and the National Institute for Communicable Diseases.</span></em></p><p class="fine-print"><em><span>Shüné Oliver receives funding from the National Research Foundation and the Female Academic Leadership Fellowship. </span></em></p>It is estimated that half of world’s population is at risk of being infected by an arbovirus.Jaishree Raman, Principal Medical Scientist and Head of Laboratory for Antimalarial Resistance Monitoring and Malaria Operational Research, National Institute for Communicable DiseasesShüné Oliver, Medical scientist, National Institute for Communicable DiseasesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1388612020-06-02T04:47:03Z2020-06-02T04:47:03ZThe next global health pandemic could easily erupt in your backyard<figure><img src="https://images.theconversation.com/files/338733/original/file-20200601-78867-6bv9ht.jpeg?ixlib=rb-1.1.0&rect=0%2C346%2C2008%2C1054&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Flickr</span></span></figcaption></figure><p>We know the virus that causes COVID-19 is linked to very similar viruses in bats, possibly passed to humans via an intermediate species <a href="https://advances.sciencemag.org/content/early/2020/05/28/sciadv.abb9153">such as pangolins</a>. The chance of a similar pandemic breaking out in Australia might seem far-fetched. But in fact, we tick all the boxes.</p>
<p><a href="https://www.nature.com/articles/s41467-017-00923-8">Hotspots</a> for emerging infectious diseases exist where human activities collide with a richness of animal species – and hence, high rates of microbial biodiversity. </p>
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Read more:
<a href="https://theconversation.com/most-laws-ignore-human-wildlife-conflict-this-makes-us-vulnerable-to-pandemics-135191">Most laws ignore ‘human-wildlife conflict’. This makes us vulnerable to pandemics</a>
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<p>As <a href="https://www.nature.com/articles/s41467-017-00923-8">research</a> has shown, Australia is such a place. Across the continent, particularly the east coast, natural landscapes have been <a href="https://www.wenfo.org/aer/#gallery-3">severely damaged</a> by human activity such as land clearing and <a href="https://www.theguardian.com/environment/ng-interactive/2018/apr/05/murray-darling-when-the-river-runs-dry">mismanagement of river systems</a>. This has led to forest loss, drying wetlands, biodiversity decline and bushfires.</p>
<p><a href="https://www.discovermagazine.com/health/coronaviruses-often-start-in-animals-heres-how-those-diseases-can-jump-to">All animals</a> harbour viruses and other pathogens. And when <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1247383/?tool=pmcentrez&report=abstract">environmental pressures</a> force animals into contact with humans, the results can be catastrophic. </p>
<h2>A world of disease</h2>
<p>In humans, around <a href="https://environmentlive.unep.org/media/docs/assessments/UNEP_Frontiers_2016_report_emerging_issues_of_environmental_concern.pdf">three-quarters</a> of all emerging infectious diseases are spread by non-humans. A new infectious disease emerges in humans <a href="http://ebrary.ifpri.org/cdm/ref/collection/p15738coll2/id/126825">every four months</a>. </p>
<p>In Africa, <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/mam.12173">the Ebola virus</a> resulted from human contact with fruit bats, and AIDS was caused by a pathogen that jumped from non-human primates <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1247383/?tool=pmcentrez&report=abstract#b61-ehp0112-001092">during road-building</a>. </p>
<p>In the United States, <a href="https://www.mayoclinic.org/diseases-conditions/lyme-disease/symptoms-causes/syc-20374651">Lyme disease</a> is caught from deer ticks. And the brain-damaging <a href="https://academic.oup.com/cid/article/34/Supplement_2/S48/459309">Nipah virus</a> originated in Malaysia after bats infected pigs, which passed the disease to farmers.</p>
<p>In China and elsewhere, the deforestation of pangolin habitat makes them easy targets for <a href="https://theconversation.com/400-000-african-pangolins-are-hunted-for-meat-every-year-why-its-time-to-act-111540">hunters and poachers</a>, who covet the animals for their meat and scales.</p>
<h2>Australia is not immune</h2>
<p>In Australia, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3734451/">a 2013 review</a> found at least 20 human diseases associated with disturbed natural environments between 1973 and 2010. They include:</p>
<p><strong>Hendra virus</strong>: This virulent disease first broke out at a racing stable <a href="https://www.business.qld.gov.au/industries/service-industries-professionals/service-industries/veterinary-surgeons/guidelines-hendra/incident-summary">in Hendra</a>, Brisbane in 1994. It causes catastrophic neurological and respiratory symptoms in horses, and more than 100 died. Seven people have been infected, four of whom died. </p>
<p>The virus is endemic to Australian flying foxes. It spilled over to people via horses who ate pasture containing flying-fox urine. <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0209798">Habitat loss</a> forced flying foxes to move close to humans to find food. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=460&fit=crop&dpr=1 754w, https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=460&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/338734/original/file-20200601-78845-1xjvsnd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=460&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Biosecurity officers taking a swab from a horse during the 2008 Hendra virus outbreak.</span>
<span class="attribution"><span class="source">Dave Hunt/AAP</span></span>
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<p><strong>West Nile virus</strong>: This causes brain inflammation and death in <a href="https://www.who.int/news-room/fact-sheets/detail/west-nile-virus">humans, horses and birds</a>. An endemic strain in Australia is transmitted by mosquitoes from wild birds. In 2011 an outbreak affected <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4982165/">about 900 horses</a> in southeastern Australia of which about <a href="https://www.horsetalk.co.nz/2019/10/30/virulent-west-nile-virus-australia/">ten per cent died</a>. </p>
<p>The virus emerged in Australia unexpectedly, probably due to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4982165/">changed environmental conditions</a> such as climate change and habitat clearing.</p>
<p><strong>Australian bat lyssavirus</strong>: <a href="https://www.ncbi.nlm.nih.gov/pubmed/32311218">this rabies-like virus</a> can be transmitted from bats to humans, causing <a href="http://conditions.health.qld.gov.au/HealthCondition/condition/14/217/10/australian-bat-lyssavirus">serious illness</a> leading to paralysis, delirium, convulsions and death. </p>
<p>A vaccine administered after exposure can prevent the virus from taking hold. But since 1996, three people who did not receive the vaccine after being bitten or scratched by bats died of the virus. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=570&fit=crop&dpr=1 600w, https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=570&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=570&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=716&fit=crop&dpr=1 754w, https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=716&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/338737/original/file-20200601-78885-igzpso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=716&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">A severe case of Buruli ulcer, which is on the rise in regional Victoria.</span>
<span class="attribution"><span class="source">Medical Journal of Australia</span></span>
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<p><strong>Buruli ulcer</strong>: <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5749465/?tool=pmcentrez&report=abstract">this disease</a>, also known as Bairnsdale ulcer and Daintree ulcer, is caused by a bacterium that destroys skin cells, small blood vessels and the fat under the skin. It causes long-term deformities. The bacterium, <em>Mycobacterium ulcerans</em>, occurs naturally in mosquitoes, vegetation and some possum droppings.</p>
<p>Australia is the <a href="https://wildlifehealthaustralia.com.au/Portals/0/Documents/FactSheets/Public%20health/Mycobacterium_ulcerans_disease.pdf">only developed country</a> with significant local transmission of Buruli ulcer and the only country to report the disease in wild animals such as possums. The number of people infected in Australia recently increased significantly in Victoria, to <a href="https://wildlifehealthaustralia.com.au/Portals/0/Documents/FactSheets/Public%20health/Mycobacterium_ulcerans_disease.pdf">340 new cases in 2018</a>. </p>
<h2>Australia: a disease-risk hotspot</h2>
<p>A <a href="https://www.nature.com/articles/s41467-017-00923-8">map</a> published in Nature Communications in 2017 showed Australia’s east coast to be a global hotspot for risk of emerging infectious diseases. </p>
<p>Australia continues to lose forest cover at alarming rates and biodiversity is suffering unprecedented decline and disruption. This <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2019.2736">increases the probability</a> of animal-human interaction. </p>
<p><a href="https://www.researchgate.net/publication/229789364_Drought-induced_mosquito_outbreaks_in_Wetlands">Drying wetlands</a> such as in the <a href="https://www.theguardian.com/environment/ng-interactive/2018/apr/05/murray-darling-when-the-river-runs-dry">Murray Darling Basin</a> destroy mosquito competitors such as aquatic animals that eat mosquito larvae. This allows mosquitoes to emerge in large numbers when water returns. This may trigger the emergence of infections such as the debilitating <a href="https://theconversation.com/explainer-the-chikungunya-virus-and-its-risk-to-australia-16968">chikungunya virus</a>.</p>
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Read more:
<a href="https://theconversation.com/australias-drought-could-be-increasing-q-fever-risk-but-there-are-ways-we-can-protect-ourselves-112297">Australia’s drought could be increasing Q fever risk, but there are ways we can protect ourselves</a>
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<p>Environmental damage can also make humans more susceptible to the effects of infectious diseases. For example, bushfires (driven in part by human-caused climate change) trigger smoke plumes that <a href="https://theconversation.com/wildfire-smoke-worsens-coronavirus-risk-putting-firefighters-in-extra-danger-136016">increase</a> the risk of dying from coronavirus. </p>
<p>Such diseases can also be catastrophic for species other than humans. <a href="https://www.sciencedirect.com/science/article/abs/pii/S1754504815001208">Chytrid fungus</a>, the most devastating disease on record to affect vertebrates, was first found in Australia in the 1970s. It had emerged in the early 20th century <a href="https://science.sciencemag.org/content/360/6389/621">on the Korean Peninsula </a>, alongside a commercial trade network in amphibians. It <a href="https://www.sciencedirect.com/science/article/abs/pii/S0006320717304020">continues to cause the extinction</a> of amphibian species worldwide. </p>
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<img alt="" src="https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/338735/original/file-20200601-78875-15eqxfl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Drying wetlands in the Murray Darling basin increase the risk of disease outbreak.</span>
<span class="attribution"><span class="source">Dean Lewins/AAP</span></span>
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<h2>What goes around comes around</h2>
<p>It’s clear human health depends on healthy ecosystems. But this undeniable fact is too often overlooked in policy decisions that allow environmental destruction. </p>
<p>Australia is an environmental and disease-risk hotspot. As a recent <a href="https://www.dea.org.au/wp-content/uploads/2020/05/Open-letter---EPBC-Review-.pdf">open letter</a> from prominent health leaders warned, the failure to conserve our environment dismantles our life-support systems and accelerates catastrophic climate change. </p>
<p>For humans to survive in our rapidly changing world, we must urgently strengthen and link policies of human health, environment and climate reform. </p>
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Read more:
<a href="https://theconversation.com/from-the-bushfires-to-coronavirus-our-old-normal-is-gone-forever-so-whats-next-134994">From the bushfires to coronavirus, our old 'normal' is gone forever. So what's next?</a>
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<img src="https://counter.theconversation.com/content/138861/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bill Laurance receives funding from the Australian Research Council and other scientific and philanthropic sources. He is director of the Centre for Tropical Environmental and Sustainability Science at James Cook University, and founder and director of ALERT -- the Alliance of Leading Environmental Researchers & Thinkers.
</span></em></p><p class="fine-print"><em><span>Penny van Oosterzee does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Australia has been identified as a hotspot for emerging diseases, which occurs when human activities collide with a richness of animal species.Penny van Oosterzee, Adjunct Associate Professor James Cook University and University Fellow Charles Darwin University, James Cook UniversityBill Laurance, Distinguished Research Professor and Australian Laureate, James Cook UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1114162019-03-19T23:01:17Z2019-03-19T23:01:17ZTick, tock: The countdown to peak tick season is here<figure><img src="https://images.theconversation.com/files/264463/original/file-20190318-28496-nhhyk6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A female blacklegged deer tick crawls along a piece of straw.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>With spring comes glorious sunshine, warmer weather — and ticks.</p>
<p>Ticks and some insect pests can carry bacteria, viruses and parasites that may cause disease in humans. One in particular, the blacklegged deer tick <em>Ixodes scapularis</em>, is well-known for its ability to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5879012/">transmit the Lyme disease-causing bacterium, <em>Borrelia burgdorferi</em></a>. </p>
<p>For the most part, these ticks are inactive throughout the winter and begin to look for their next meal as seasonal temperatures warm up. </p>
<p>But as the global climate warms, it is more likely that some ticks will remain active through the warmer winters and can expand their habitats into new areas. Because of this, hikers and dog owners need to be watchful for ticks year-round to reduce the risks of getting sick.</p>
<h2>Cold adapted</h2>
<p>Ticks and other pests are prevalent in forests during the warmer months, from spring to fall. But where do they go during the winter and how do they survive the cold polar vortexes, inches of snow and frostbite-inducing windchill?</p>
<p>Animals use a variety of strategies to deal with the winter months. While humans layer on clothing and mostly avoid going outside during bone-chilling temperatures, other organisms employ sophisticated behavioural adaptations and biological technologies to face winter head-on. </p>
<p>For the common house mosquito <em>Culex pipiens</em>, hibernation is key to survival. The insect enters a dormant phase (called diapause) allowing it to stay mostly inactive through the winter. The female <em>Culex</em> mosquito, a possible carrier of the West Nile virus, builds up fat stores during the summer and fall that serve as energy reserves and insulation for the winter months. This source of energy is useful for mosquitoes after they seek out and settle down in the human-made structures, sewers and animal burrows that they use as shelter to help them <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2373331/">escape subzero temperatures</a>. </p>
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<img alt="" src="https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264643/original/file-20190319-60949-yy29y3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Blacklegged ticks position themselves at the tips of grasses to seek out their next blood meal such as from passing dogs.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
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<p>Ticks, however, don’t enter diapause and are still able to bite and eat a blood meal under the right conditions. These blood-sucking parasites live close to their host organisms, and can sometimes spend their entire life cycle on one animal. They use a technique called questing to locate a host that will serve as their next blood meal. Ticks station themselves on vegetation such as tall grasses and assume a sit-and-wait position. This allows them to grab onto any warm-blooded creature passing by. </p>
<p>Humans have employed our own behavioural strategies to protect ourselves from ticks during the warm seasons of the year. We do this by wearing long-sleeved clothing and using protective sprays when going on hikes through wooded and grassy areas. </p>
<h2>Battle against the bite</h2>
<p>One of the main challenges we still face in our battle against the bite is the fact that ticks further adapt their behaviour depending on where they are located in North America. </p>
<p>For instance, blacklegged deer ticks will avoid questing in warmer southern regions such as in South Carolina, where the risk of dehydration pushes them onto the ground, mostly below the leaf litter. In contrast, northern tick populations are less threatened by drying out due to humid conditions, and are <a href="http://europepmc.org/articles/pmc5226345">more likely to quest</a>. </p>
<p>Interestingly, blacklegged deer ticks also have the ability to quest in <a href="https://academic.oup.com/jme/article/38/2/318/877734">temperatures as low as -0.6°C</a>. This means that deer ticks are not limited to seeking out hosts during the warm months alone, but can continue feeding well into the early and late winter. It is therefore important not to lower one’s guard when enjoying the outdoors in wintertime. </p>
<p>Ticks are most active when temperatures rise above 7°C. But don’t be fooled into thinking that ticks simply die when the harsh winter weather kicks in! In reality, deer ticks are likely to survive even the harshest polar vortex. </p>
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Read more:
<a href="https://theconversation.com/ticks-and-mosquitoes-bringing-more-diseases-what-can-we-do-96688">Ticks and mosquitoes bringing more diseases – what can we do?</a>
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</em>
</p>
<hr>
<p>It is quite common for ticks to cluster in hibernation nests and seek refuge under the layer of soil and ground litter within forests, where the temperature is less likely to fall below zero. In addition, snow cover, which acts like an insulating blanket over ground litter, tends to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4844560">further insulate ticks</a> from the frigid winter air temperatures. </p>
<p>Much like other cold-tolerant organisms, ticks can also produce an <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929727/">antifreeze protein</a> that helps them tolerate colder temperatures by preventing their blood and tissues from freezing.</p>
<h2>Looking forward</h2>
<p>Climate change and the warming of our planet have resulted in the expansion of blacklegged deer tick populations to more northern regions of North America, including the the states of Wisconsin and New York and the provinces of Ontario and Québec. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=435&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=435&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=435&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=547&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=547&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264639/original/file-20190319-60959-1chnzik.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=547&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The characteristic bull’s-eye patterned rash after the bit from a blacklegged tick infected with <em>Borrelia burgdorferi</em>.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>Using climate change models and current tick distribution patterns, we can <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5730520/">now predict the impact of future climate change on the migration of ticks</a> and the potential health risks that these populations carry across Canada and the <a href="https://tickencounter.org/current_tick_activity">United States</a>. For example, the geographic distribution of the blacklegged tick is projected to expand and cover most of Atlantic Canada and Manitoba by the year 2070. </p>
<p>It is very likely that all seasons can be a tick season in some regions. This makes it especially important to engage in continued vigilance in spotting and avoiding these tiny pests, even when out for a walk during the winter months. If your dog disrupts a patch of nested deer ticks for example, it could bring home some unwanted guests. </p>
<p>So, what can we expect as the weather warms up and as long winter nights transition into sunnier spring days? You can be certain that a large number of ticks that were around last season likely survived this winter. They are simply waiting for the right cues — warmer temperatures and longer daylight hours — to emerge and begin their quest for their next blood meal.</p><img src="https://counter.theconversation.com/content/111416/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rosa da Silva is an Assistant Professor in the Department of Biology and School of Interdisciplinary Science at McMaster University.
Rosa da Silva has previously received funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p>Ticks are generally inactive in the winter and start to look for their next meal as temperatures warm up. But as winters warm, every season may become tick season.Rosa da Silva, Assistant Professor, McMaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1055502018-12-04T11:33:13Z2018-12-04T11:33:13ZOpening up research labs with modified mosquitoes to the community<figure><img src="https://images.theconversation.com/files/244375/original/file-20181107-74757-1b7ob0j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">View of Taichung City, Taiwan, behind a mosquito net. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/view-mosquito-net-taichung-city-taiwan-662487235?src=eoF5QMrNkj4UaA26ScSy2A-4-8">Alan Picard / Shutterstock.com</a></span></figcaption></figure><p>By bringing people close to disease-spreading insects, might we improve public health?</p>
<p>Because they spread malaria, Zika, West Nile, dengue, yellow fever and other diseases, mosquitoes are <a href="https://www.smithsonianmag.com/innovation/kill-all-mosquitos-180959069/">responsible for more human deaths than any other organism</a>. Some of these diseases flourish in tropical regions like sub-Saharan Africa that are urbanizing rapidly and feeling the effects of climate change. Research indicates that <a href="https://doi.org/10.1016/j.jclepro.2017.12.144">temperature increases</a> lead to mosquitoes breeding more frequently, living longer and biting more often. </p>
<p>Meanwhile, advances in scientific research are leading to new approaches to mosquito control. These include <a href="https://www.newyorker.com/magazine/2012/07/09/the-mosquito-solution">genetic</a> <a href="https://www.scientificamerican.com/article/the-wipeout-gene/">modification</a> of male mosquitoes, leading to sterile offspring. Scientists are also exploring the <a href="http://doi.org/10.1016/j.pt.2015.10.011">use of bacteria such as <em>Wolbachia</em></a> to limit the ability of mosquitoes to spread disease. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/244382/original/file-20181107-74766-n4vd3g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mosquito research facilities are often cloaked in secrecy which breeds distrust among the public.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/mosquito-testing-center-infected-germs-628430486">Aomboon / Shutterstock.com</a></span>
</figcaption>
</figure>
<p>But mosquito research faces one enormous challenge: a lack of community engagement around this science leads to the <a href="https://theconversation.com/gene-drives-may-cause-a-revolution-but-safeguards-and-public-engagement-are-needed-77012">public feeling anxiety and mistrust</a>. Negative public opinion has the potential to derail this research and associated efforts, such as release of genetically modified mosquitoes in cities. My colleague John Bauer, assistant dean for the UC San Diego Division of Biological Sciences, noted to me that scientists work in high security buildings that the public are banned from entering and then wonder why they are so misunderstood. </p>
<p>I am a professor of architecture at the University of Oregon and am involved in an effort to re-imagine these mosquito research facilities and make them accessible to the public. In an effort to do so we have convened teams of designers, artists and scientists to rethink the design of mosquito research sites so that they include spaces of community engagement. </p>
<h2>Making genetic research transparent</h2>
<p>I have long worked at the <a href="http://www.worldcat.org/title/ecology-and-the-architectural-imagination/oclc/854611173">intersection of people and the environment</a>. I am now working together with <a href="http://www.michaelsinger.com">artist Michael Singer</a>, <a href="https://www.researchgate.net/profile/Mark_Benedict2">Mark Benedict</a> of the Centers for Disease Control and Prevention’s Entomology Branch, <a href="https://ihi.or.tz/staff/dr-fredros-okumu">Fredros Okumu</a> from Tanzania-based <a href="https://ihi.or.tz">Ifakara Health Institute</a> (IHI), and scholars and scientists from the U.K. and U.S., on the “Protective Atmospheres” project to redesign these facilities. </p>
<p>This has the potential to be a game-changing effort. Our hope is that opening up the facility will lead to greater acceptance of this work and lead to better health outcomes. My collaborators and I are not aware of any similar effort meant to integrate research facilities and the community in order to make science approachable.</p>
<p>This is where effective design comes in. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=285&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=285&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=285&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=358&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=358&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245814/original/file-20181115-194513-1vieixh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=358&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An artist rendition of a research facility integrated with the community.</span>
<span class="attribution"><span class="source">Brook Muller</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=160&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=160&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=160&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=201&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=201&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245815/original/file-20181115-194513-16c7sg0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=201&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Integrating labs with open fields may reduce the fear factor surrounding mosquito research.</span>
<span class="attribution"><span class="source">Brook Muller</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>What if “arthropod containment” labs with strict biosecurity standards where scientists work with pathogen-carrying mosquitoes are not located at the “back of house” as is typical now. While ensuring that these standards are met, could labs be brought out of the darkness and placed alongside spaces where visitors to these facilities are allowed to go? </p>
<p>Could people walk through protective enclosures alongside or within “mosquito cities,” large spaces of experimentation that are open-air yet netted and that include trees and other outdoor elements allowing controlled study of mosquito populations in quasi-natural conditions? </p>
<p>Could spaces be included that help people understand how to modify their homes to decrease chances they will get bitten? What about recreational spaces such as the tennis court that Okumu hopes to build at Ifakara as a way to make IHI’s research a part of everyday community life? These are some of the questions we are addressing as part of the Protective Atmospheres project. </p>
<h2>Integrating scientists and the community</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=480&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=480&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245849/original/file-20181115-194497-ciunx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=480&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Mosquito City Vision. The goal is not just to mix communities and lab and research facilities. Muller wants the scientists to engage with the local people over normal recreation and participate in daily life.</span>
<span class="attribution"><span class="source">Brook Muller</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Creating interactive facilities that promote public engagement and understanding while adhering to biosafety regulations requires a two-way conversation. Architects and artists must learn from scientists. As one example, they must understand that keeping mosquitoes alive in captivity is difficult. Or that for <em>Anopheles</em>, a genus of mosquito carrying malaria, the setting sun and low light triggers swarm behavior and mating. For a mosquito city built to study swarming behavior, it’s best to orient it toward the sun, and let the romance begin. </p>
<p>And scientists can learn from architects and artists that buildings can tell stories. A walk through a research facility may also be an educational journey through the scientific process along a continuum from genetic engineering to containment to release. By the time a visitor arrives at a mosquito release site at the journey’s end, it may no longer seems so dangerous. Perhaps at that point, visitors actually participate in the release event.</p>
<p>The Protective Atmospheres project is in its infancy, and yet we are hopeful that it has the potential to transform perceptions. It can make scientific activity transparent and encourage the role of citizenry in biological research. It might also change understandings of mosquitoes themselves – for mosquitoes do not kill, they just host organisms that do. </p>
<p>The end game of course is to build one of these facilities. When we do, we hope that children – and others – line up to visit. Concept shifts to reality when members of the Michael Singer Studio and I travel to the Ifakara Health Institute in early 2019 to begin the development of a master plan for their complex. It will include a tennis court.</p><img src="https://counter.theconversation.com/content/105550/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brook Muller works for the University of Oregon. </span></em></p>Genetically modified mosquitoes breed fear and suspicion, especially since the research happens behind closed doors, away from the public. Now scientists and architects are trying to change that model.Brook Muller, Professor of Architecture and Environment, University of OregonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/983692018-06-21T21:55:05Z2018-06-21T21:55:05ZWhy your summer might be full of mosquitoes, according to a scientist<figure><img src="https://images.theconversation.com/files/224325/original/file-20180621-137734-ib3jp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The tiny mosquito can be a big summer nuisance.</span> <span class="attribution"><span class="source">(Pexels)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>As you pack your bags for the cottage or campground this weekend, don’t forget to bring light clothes with long sleeves — and a truckload or two of insect repellent. </p>
<p>Spring has come and gone, so welcome to mosquito season. </p>
<p>How much we enjoy summer in North America depends a lot on how many mosquitoes there are waiting for us outside. Their bites are itchy and their drone annoying, but there’s also concern that mosquitoes carrying dangerous diseases are knocking on our door. </p>
<p>So what makes some years worse than others?</p>
<h2>Is it a good year for mosquitoes?</h2>
<p>You don’t have to be an entomologist (a.k.a. an insect scientist) to notice that the mosquito population size can vary from year to year and place to place.</p>
<p>Last June, I couldn’t set foot <a href="http://www.cbc.ca/news/canada/ottawa/flooding-mosquitoes-kanata-north-control-program-1.4115976">outside my Ottawa</a> home without being bitten. Meanwhile, Winnipeg was experiencing its <a href="http://www.cbc.ca/news/canada/manitoba/mosquitoes-trap-counts-winnipeg-1.4181194">lowest mosquito count</a> in four decades. </p>
<p>This year is far from mosquito-free, but I can at least enjoy peace for about 10 minutes before they find me.</p>
<p>What causes mosquito populations to balloon and shrink? In short, it’s a combination of weather and climate — mosquitoes are <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/04-1248">very sensitive</a> to their environment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224274/original/file-20180621-137734-b7j5u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Will your weekend be itchy or not?</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>Temperature and rainfall are <a href="https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/eap.1405">two major predictors</a> of mosquito abundance, and this is for a good reason: These two factors have a massive effect on their survival and ability to reproduce. </p>
<p>How much it rains at one time, when it rains, how long a cold or warm spell lasted and when it happened all matter when it comes to predicting what kind of mosquito season lies ahead. </p>
<h2>Mosquitoes like it warm and wet</h2>
<p>Mosquitoes, like most insects, are cold-blooded, or ectothermic. Unlike us, their body temperature closely matches the temperature of the environment (air or water) around them. If it is cold outside, they are cold. If it is warm outside, they are warm. Any time spent outside of their comfort zone can slow or stop their development or even cause them to be <a href="https://www.annualreviews.org/doi/10.1146/annurev-physiol-022516-034142">injured and die</a>.</p>
<p>In order for most mosquito larvae to grow, temperatures need to be above a threshold, which varies, depending on the species, but is typically around <a href="https://www.tandfonline.com/doi/abs/10.1080/00222933.2011.590946">seven</a> to <a href="https://www.cambridge.org/core/services/aop-cambridge-core/content/view/6375ECAEF9B542ABB63F074E0972C855/S0007485303000440a.pdf/effect_of_temperature_on_the_development_of_the_aquatic_stages_of_anopheles_gambiae_sensu_stricto_diptera_culicidae.pdf">16 degrees Celsius</a>. </p>
<p>Since the larvae are entirely aquatic, they also need a source of standing water (like your flower pot) that will remain until they are ready to emerge as adults. </p>
<p>This means cold or dry conditions that hit at the right time during larval development in the spring or summer can drastically reduce the number of adult mosquitoes looking for a meal a week or two later.</p>
<h2>Human hunters, disease spreaders</h2>
<p>We love to hate mosquitoes, but the vast majority of mosquito species do not directly impact our lives.</p>
<p>Mosquitoes, like most insects, are outrageously diverse: There are more than <a href="https://www.mosquito.org/general/custom.asp?page=mosquitoinfo">3,000 species</a> of mosquitoes buzzing about on this planet, and only a handful of those species actively hunt humans. </p>
<p>And even then, only female mosquitoes feed on blood. The much more reasonable males instead drink flower nectar.</p>
<p>Unfortunately, some of these mosquito species are also far from being just a mild annoyance, as they can carry dangerous diseases. In Canada and the United States, we often hear about the threat of West Nile virus, which is <a href="http://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1000092">carried by local mosquito species</a> and can lead to serious health complications like coma and paralysis in a minority of cases. </p>
<p>One of the best predictors of West Nile infection rates in Ontario is the <a href="https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-018-3052-6">minimum temperature</a> reached during February. If the coldest temperatures in February are warmer than usual, more people become infected with West Nile virus during the summer months.</p>
<p>In tropical regions, people instead contend with malaria, yellow fever, dengue, chikungunya and Zika viruses. These viruses are all spread by mosquitoes, are severely debilitating and cause hundreds of thousands of deaths each year. </p>
<p>When Hurricane Harvey hit Texas in September 2017, the flooding increased the mosquitoes’ breeding habitat. So, the state sprayed 240,000 hectares around Houston to help <a href="https://www.the-scientist.com/?articles.view/articleNo/50333/title/After-Harvey--Mosquito-Control-Ramps-Up/">prevent an increase in mosquito-borne disease</a>.</p>
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Read more:
<a href="https://theconversation.com/viruses-can-cause-global-pandemics-but-where-did-the-first-virus-come-from-94551">Viruses can cause global pandemics, but where did the first virus come from?</a>
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<p>The fact that mosquitoes carry these diseases, rather than the mosquitoes themselves, led the Gates Foundation to label mosquitoes the <a href="https://www.gatesnotes.com/Health/Most-Lethal-Animal-Mosquito-Week">deadliest animals</a> on the planet.</p>
<p>Two of the worst offenders for spreading disease are the yellow fever mosquito (<em>Aedes aegypti</em>) and the Asian tiger mosquito (<em>Aedes albopictus</em>), which typically live in <a href="https://elifesciences.org/articles/08347">tropical and subtropical regions</a> where it stays warm and humid. The range of these mosquitoes also extends well into the continental U.S., <a href="https://www.cdc.gov/zika/vector/range.html">particularly in the southern and eastern states</a>. However, they simply cannot survive northern climates with long and cold winters.</p>
<h2>Tinkering with climate</h2>
<p>Suitably low winter temperatures typically keep tropical and subtropical insect species from becoming permanently established in areas closer to the poles with cold winters. Over the past few decades, however, climate change has led to documented changes in insect distribution patterns, including the <a href="http://science.sciencemag.org/content/sci/349/6244/177.full.pdf">collapse of southern range limits</a> of bumblebees and the <a href="http://science.sciencemag.org/content/333/6045/1024.long">northward movement of many insect ranges</a>.</p>
<p>As winters become more mild, the northern limits of mosquito ranges may also be shifting. Movement of the northern range limits are <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12105">thought to happen</a> because milder winters allow species that can’t usually hack it in the cold to squeak through winter alive, reproduce and establish themselves in a new location. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/224219/original/file-20180621-137708-1mfaho3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The Asian tiger mosquito, which can transmit the Zika virus, has been spotted in southern Ontario in Canada.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
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<p>Mosquito trapping programs are active around the globe, precisely because monitoring and responding to mosquito populations is critical to global health. In the last few years (2016-2018), adults of both the yellow fever mosquito and the Asian tiger mosquito were found in <a href="https://www.wechu.org/newsroom/news-release-mosquito-trap-reveals-2-aedes-albopictus-species-area">Windsor, Ont.</a> (near the southernmost point of Canada), which suggests that these dangerous vectors could be a serious health concern in northern climates in the future. </p>
<p>Thankfully, none of the individual mosquitoes caught in Windsor have tested positive for any viruses.</p>
<p>In an era of climate change, it’s increasingly essential that we understand what environmental factors determine where insects can and will live, and how well they do. Understanding how insects respond to climate is absolutely critical to our food security and global health. </p>
<p>Only when we are armed with this information can we accurately predict the spread of invasive agricultural pests or disease vectors, like the bloodsucking mosquitoes that even entomologists despise.</p><img src="https://counter.theconversation.com/content/98369/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Heath MacMillan receives funding from the Natural Sciences and Engineering Research Council of Canada to study the physiological mechanisms of thermal injury in insects. </span></em></p>Mosquito abundance is linked to climate and weather, and global climate change may be helping spread these dangerous carriers of disease.Heath MacMillan, Assistant Professor of Biology, Carleton UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/855892017-10-23T22:52:29Z2017-10-23T22:52:29ZExplainer: How we all benefit from the public health system<p>Despite major breakthroughs in antibiotics and vaccinations, <a href="https://theconversation.com/canada-could-lead-the-fight-for-life-in-a-post-antibiotic-world-80864">infectious disease threats</a> continue to emerge in Canada.</p>
<p><a href="https://globalnews.ca/news/3489775/federal-government-to-pour-4-million-into-first-ever-lyme-disease-framework-heres-why/">Lyme disease</a>, <a href="http://www.cbc.ca/news/canada/kitchener-waterloo/ontario-west-nile-virus-rain-heat-2017-1.4248257">West Nile virus</a> and <a href="https://globalnews.ca/news/3356063/are-measles-outbreaks-here-to-stay-heres-what-canadas-top-doctor-thinks/">measles</a> pose ongoing challenges. An <a href="https://thetyee.ca/Opinion/2017/03/24/Tuberculosis-in-Canada/">increasing proportion of tuberculosis cases are extensively drug-resistant</a>. Earlier this year there were 473 travel-related cases and three sexually transmitted cases of the <a href="http://www.cbc.ca/news/health/zika-cmaj-canadians-complications-1.4009793">Zika virus</a> reported in Canada. And new global pandemics — exacerbated by factors such as <a href="https://healthpolicy.fsi.stanford.edu/news/civil-wars-and-global-threat-pandemics">conflict</a> and the impact of <a href="http://outbreaknewstoday.com/climate-change-may-accelerate-infectious-disease-outbreaks-colorado-researchers-14549/">climate change</a> on <a href="https://theconversation.com/climate-change-is-making-cities-sick-and-we-need-to-act-78447">cities</a> — are an ever-present possibility. </p>
<p>At the same time, injuries and chronic health conditions like heart disease and diabetes continue to take lives and inflate our health-care costs. And while the <a href="https://theconversation.com/how-healthy-is-the-canadian-health-care-system-82674">health-care system</a> seems to be our natural safeguard against these problems, there is only so much doctors and hospitals can do to maintain the health of Canadians. So who exactly is responsible for the well-being of the entire Canadian population?</p>
<p>As a PhD student of population health sciences at the University of Saskatchewan, I am researching the system delegated to this monumental task, one that is often taken for granted the world over: The public health system.</p>
<p>So what is the public health system? Who is involved and what do they do?</p>
<h2>Preventing health disasters</h2>
<p>The average Canadian will likely not even hear about the public health system unless something goes awry. This is because the public health system in Canada largely works <a href="https://www.canada.ca/en/public-health/corporate/publications/chief-public-health-officer-reports-state-public-health-canada/report-on-state-public-health-canada-2008/chapter-2a.html">to prevent health disasters from occurring</a>, while maintaining existing initiatives — such as public health inspections programs, water-quality testing and disease surveillance programs — to ensure our health.</p>
<p>The public health system in Canada operates at three levels of jurisdiction: Nationally, provincially/territorially and at the city level.</p>
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<figcaption><span class="caption">An overview of public health in Canada.</span></figcaption>
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<p>At the federal level, the Public Health Agency of Canada provides national guidance to the provinces and cities regarding the state of infectious diseases, chronic diseases and injuries in Canada. It conducts research, provides policy recommendations and supports public health programs.</p>
<p>As with most health services in Canada, the provinces are in charge of setting regulations and targets for local public health professionals. They do this by collecting and synthesizing the provincial public health data to stay ahead of disease trends and by producing province-specific public health policies and regulations.</p>
<p>In local regions, epidemiologists, nurses, doctors and inspectors — along with groups of interdisciplinary health promotion professionals — work together to investigate outbreaks, maintain local food safety and promote day-to-day healthy behaviour and public policy. The exact organizational arrangements differ between provinces.</p>
<h2>Turning data into action</h2>
<p>The Public Health Agency of Canada (PHAC) lays out <a href="http://www.phac-aspc.gc.ca/php-psp/ccph-cesp/pdfs/cc-manual-eng090407.pdf">seven core competencies</a> required of public health professionals. They include science, assessment and analysis, policy evaluation, collaboration and advocacy, diversity and inclusiveness, communication and leadership.</p>
<p>All seven describe the most effective traits for those working in public health to fulfil their mandates. These skills are similar to those defined by the <a href="https://www.cdc.gov/nceh/ehs/ephli/core_ess.htm">United States Centres for Disease Control (CDC) three fundamental purposes of public health</a>: Assessment, policy development and assurance.</p>
<p>“Assessment” involves monitoring the health status of populations and diagnosing population-based health issues. For example, it is public health officials who first detect a virus outbreak or announce increasing rates of chronic diseases based on data they receive from the health system or from their own independent investigations.</p>
<p>“Policy development” turns the data into action. This involves sharing information regarding public health issues, working with community organizations and the private sector to address emerging concerns and developing policies and programs to enable a healthy society. This work ensures that solutions are developed and deployed by public health agencies, and that they’re supported over the long-term by those living in affected communities.</p>
<p>“Assurance” involves a multi-partner effort to enforce public health laws and regulations. It involves interfacing with the health system to connect patients with services and improving the science of public health. This involves leadership, accountability and clear communication on behalf of public health officials.</p>
<h2>Social determinants too large to handle?</h2>
<p>In Canada, the social determinants of health include income, education, employment and housing. These are factors that influence people’s health status but do not necessarily involve the traditional health-care system. The Canadian Medical Association proposes that <a href="https://www.cma.ca/Assets/assets-library/image/en/advocacy/what-makes-canadians-sick-e.png">the social determinants of health are at least 50 per cent responsible for any given population’s health status</a>.</p>
<p>Because the social determinants of health generally involve social and public policy factors outside of the traditional public health mandate, questions regarding what public health should and can do complicate action.</p>
<p>The National Collaborating Centre for Determinants of Health reviewed the research and found that social determinants of health are <a href="http://nccdh.ca/images/uploads/Environ_Report_EN.pdf">often seen as too large in scope for public health to handle</a>, especially with limited resources.</p>
<p>As our understanding about the large impact of the social determinants of health increases, it is becoming clear that public health can only be achieved through the collaboration of all social and public policy spheres of influences — across economic, environmental, business and health care institutions — to move a healthy agenda forward.</p>
<h2>Increasing public health investment</h2>
<p>The rise and persistence of chronic diseases, and the re-emergence of global infectious diseases, threaten Canadians and the world alike. It is vitally important that all public health agencies work together, across jurisdictions, to maintain population health.</p>
<p>In 2014, only <a href="https://www.cihi.ca/sites/default/files/document/2016-nhex-technical-notes-on-public-health_en.pdf">5.6 per cent of total health care spending was allocated to public health</a>. As most of the public health service providers in the country exist within the larger health-care system, funding is often tied to <a href="https://www.thestar.com/opinion/commentary/2016/10/18/why-we-need-to-boost-public-health-spending.html">priorities that are not associated with long-term public health gains</a>. </p>
<p>To make gains we must reorient our understanding of health, away from sickness-care and towards prevention. This involves increasing public health investment. This should also involve a <a href="http://www.who.int/healthpromotion/frameworkforcountryaction/en/"><em>Health in All Policies</em></a> approach to governing. This calls for institutions responsible for the social determinants of health — such as government ministries in charge of finance, housing, social services and the environment — to consider the health of the population in their mandates. This will involve public health professionals working across silos to make health a societal priority.</p>
<p>There is also a general lack of detailed information about the public health work force, best practices and organizational arrangements in Canada. Promising developments in the field of <a href="http://www.publichealthsystems.org/">public health systems and service research</a> south of the border must be replicated in a Canadian context to better understand our public health landscape. </p>
<p>The more that is known about our current system, the better equipped we will be to mobilize effective practices nationally and to improve population health moving forward.</p><img src="https://counter.theconversation.com/content/85589/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thilina Bandara received funding from the Natural Sciences and Engineering Research Council of Canada/Collaborative Research and Training Experience Program for his doctoral research and is a Board Member for Upstream (<a href="http://www.thinkupstream.net">www.thinkupstream.net</a>).</span></em></p>Infectious diseases pose a continual threat to Canadians. Ensuring the population stays healthy requires increasing investment in our public health system.Thilina Bandara, PhD student, Community and Population Health Sciences, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/494752015-10-27T04:14:52Z2015-10-27T04:14:52ZThe threats humans present to wildlife through infectious diseases<figure><img src="https://images.theconversation.com/files/99646/original/image-20151026-18424-89rj7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Frog chytrid may have been spread by humans. It is a fungus that has decimated amphibian species.</span> <span class="attribution"><span class="source">Reuters</span></span></figcaption></figure><p>The threat of diseases moving from animals to people has been the focus of many studies and is well documented in public and scientific communications. 60% of infectious diseases in humans have been estimated to come from <a href="http://www.cdc.gov/onehealth/zoonotic-diseases.html">animals</a>. Nevertheless we need to be concerned about the threat that people present to the health of animals. </p>
<p>According to the Centers for Disease Control and Prevention, the health of humans is connected to the health of animals and the environment. This approach is known as the <a href="http://www.cdc.gov/onehealth/">One Health concept</a>.</p>
<p>A recent <a href="http://planetearth.nerc.ac.uk/news/story.aspx?id=1698">study</a> suggests animals that have been domesticated for longer periods of time are more likely to share their diseases with humans. And we’ve witnessed the devastating <a href="http://onlinelibrary.wiley.com/doi/10.15252/emmm.201404792/pdf">diseases</a> that have emerged from wildlife hosts to affect humans – including the Ebola virus, Hantavirus, SARS, and human immunodeficiency virus (HIV). Yet the impact that the increasing presence of humans and domestic animals in previously pristine habitats has on wildlife is under-reported.</p>
<h2>People spread diseases unintentionally</h2>
<p>Pathogens usually co-evolve with their hosts. This means they reach a balance within a population so that a species will develop defences resulting in co-existence of pathogen and host. But when new interfaces between species occur or there is a disturbance in the ecosystem, this balance may be upset. This results in increased vulnerability to emerging <a href="https://wwww.nwf.org/Wildlife/Threats%20-to=Wildlife/Diseases.aspx">diseases</a>.</p>
<p>An example of this is in chytrid fungus (Bactrachochytrium dendrobatidis) that causes a <a href="http://www.savethefrogs.com/threats/chytrid/">lethal skin disease</a> to amphibian populations <a href="http://www.amphibianark.org/the-crisis/chytrid-fungus/">globally</a>. Some species, like American bullfrogs and African clawed frogs, are resistant to the <a href="http://www.amphibianark.org/the-crisis/chytrid-fungus/">fungus</a>. The accidental or intentional movement of these animals may lead to the introduction of the disease to naïve frog populations. </p>
<p>In the case of some frog species there are a number of human factors which have led to the spread of the disease. These factors have also contributed to the extinctions of some populations. The factors include: global trade in pet and laboratory amphibians, habitat destruction, and the transfer of fungus on equipment and boots of people entering habitats.</p>
<p>People have moved their livestock and pets for centuries. This is not a new phenomenon, as diseases have been introduced to native peoples and wildlife during the European exploration of the New World, the colonisation of Africa, and the establishment of trade routes to the <a href="http://www.jareddiamond.org/Jared_Diamond/Guns,_Germs,_and_Steel.html">Far East</a>.</p>
<h2>The diseases that are spread</h2>
<p>Humans are reservoirs of many diseases. They have an impact on diseases in wildlife through direct interaction as well as indirect activities. </p>
<p>Direct interaction with wild animals include ecotourism, bushmeat hunting, research, and the movement of pets – which carries a risk of disease spread in both directions. </p>
<p>Endangered gorillas live in the mountains of Rwanda, Uganda, and the Democratic Republic of the Congo. They are surrounded by some of the densest human communities in Africa. As a result there has been regular contact between these animals and humans because of: habituation, gorilla movement, human encroachment and beneficial research programs. This has brought these animals into close proximity with people and their pathogens. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=365&fit=crop&dpr=1 600w, https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=365&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=365&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=459&fit=crop&dpr=1 754w, https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=459&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/99643/original/image-20151026-18443-rcg2q2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=459&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">From continued interaction with humans mountain gorillas have suffered a decline in numbers because of measles.</span>
<span class="attribution"><span class="source">Thomas Mukoya/Reuters</span></span>
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</figure>
<p>As a result, respiratory infections and parasites have spread. Disease outbreaks and fatalities have been <a href="http://wwwnc.cdc.gov/eid/article/17/4/10-0883">recorded</a> in gorillas due to measles and bacterial pneumonia. We’ve also seen poliomyelitis and measles in wild chimpanzees in <a href="http://www.nytimes.com/2013/08/02/opinion/apes-need-vaccines-too.html?_r=0.ls">Tanzania</a>.</p>
<p>Human tuberculosis (TB), caused by Mycobacteria tuberculosis, is another disease which <a href="http://www.sanparks.co.za/parks/kruger/conservation/scientific/noticeboard/science_network_meeting_2008/Friday/michel.pdf">affects</a> a wide variety of wild animals, including chimpanzees, elephants and rhinoceros. </p>
<p>Although most cases have occurred in captivity, the increased contact between wildlife and humans in these settings presents a risk to animal health. There is also a disease risk in semi-captive situations where animals may also interact with their wild counterparts, especially in countries with a high rate of TB like <a href="http://www.rense.com/general77/eleph.htm">Nepal</a>. </p>
<p>Human TB has been recognised as the cause of deaths in working elephants in Nepal. Awareness has allowed implementation of programs to prevent spread from humans to elephants and minimise the impact of the disease on the <a href="http://www.ntnc.org.np/sites/default/files/publicaations/Nepal%20Elephant%20TB%20Control%20and%20Mgt%20Action%20Plan.pdf">elephants</a>.</p>
<p>Bovine tuberculosis caused by Mycobacterium bovis in cattle was initially recognised in South Africa in 1880, where it is considered an alien disease. By 1928, the first cases were identified in a greater kudu and common duiker. In less than 100 years, this disease has been <a href="http://theconversation.com/why-bovine-tb-is-a-threat-to-more-than-just-cattle-42336xx">found</a> in more than 21 different wildlife species in South Africa.</p>
<p>Bovine tuberculosis has also become established in other populations worldwide. These include badgers and wild boars in Europe, deer in North America, and brush-tailed possums in <a href="http://vet.sagepub.com/content/50/3/488.long">New Zealand</a>.</p>
<p>Indirect activities stem from human development in previously pristine habitats, global travel and climate change. This too has resulted in the increased risk of disease transmission through indirect activities. For example, the human protozoal parasite, Giardia duodenalis, has been <a href="http://www.cfsph.iastate.edu/Factsheets/pdfs/giardiasis.pdf">found</a> in the endangered African wild dogs, mountain gorillas, and beavers. It is believed that people contaminate the environment, resulting in exposure of animals through sewage runoff.</p>
<p>Other less apparent indirect impacts caused by humans include movement or expansion of geographical boundaries for disease vectors such as mosquitoes. The <a href="http://www.cdc.gov/westnile/">West Nile Virus</a> was introduced to the US in 1999, probably as a result of movement of an infected bird or mosquitoes, or possibly travel of an infected <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2094770/">human</a>. </p>
<p>Since that time, massive mortalities have occurred in wild birds, and other native and non-native wildlife in the US. There has also been serious health consequences for horses and humans.</p>
<p>Increased knowledge is needed to understand the role that humans play in diseases of domestic and wild animals. We may contribute to emerging diseases through climate change, habitat use, global and local movements of species, and interactions with animals and their environment. We need to understand better how to mitigate the effects of disease on our <a href="http://www.sun.ac.za/english/faculty/healthsciences/Molecular_Biology_Human_Genetics/animaltb">wildlife</a>.</p><img src="https://counter.theconversation.com/content/49475/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michele Miller receives funding from the South African National Research Foundation. </span></em></p>As much as animals may pass on viruses to humans, humans pass on viruses which are sometimes lethal to the animal world as well.Michele Miller, Research Chair in Animal Tuberculosis, Stellenbosch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/443972015-07-10T05:25:42Z2015-07-10T05:25:42ZEnjoying the weather? Well look out, mosquitoes love it too<figure><img src="https://images.theconversation.com/files/87910/original/image-20150709-10895-185sdi7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Which way to the bar?</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>A hot summer brings out the sunglasses, ice cream and <a href="https://theconversation.com/are-you-beach-feet-ready-42982">bare feet</a>. Unfortunately it also brings out the flying, biting pests. The UK has <a href="http://www.dipteristsforum.org.uk/">7,000 species</a> of flies, including midges, horse flies and the ones with arguably the worst reputation, mosquitoes.</p>
<p>The most common mosquito species in the UK is <em>Culex pipiens</em>. Few people are actually bitten by it, since it mainly feeds on birds, but this year there are <a href="http://metro.co.uk/2015/06/08/its-going-to-be-a-scorching-summer-and-that-means-more-mosquitoes-5236245/">likely to be more</a> <em>C. pipiens</em> and other mosquito species than usual. This is down to seasonal conditions. Pregnant female mosquitoes hibernate and the mild winter will have resulted in greater survival – and more eggs. A wet May was ideal for the aquatic larvae. A hot summer means more fly activity and more people outside to be bitten. So the cycle continues. </p>
<p>Mosquitoes have needle-like mouth parts that pierce flesh so they can suck blood. They also secrete anticoagulants that prevent clotted blood blocking their mouth parts, and a local anaesthetic so you can’t feel the bite. But these bites aren’t just annoying – they’re potentially deadly.</p>
<p>Mosquito saliva can be a vehicle for transmission of diseases such as malaria, caused by a tiny protozoan organism called Plasmodium. In 2013, between 124m and 283m people contracted the disease and an estimated <a href="http://www.who.int/mediacentre/factsheets/fs094/en/">584,000 people died from it</a>.</p>
<p>As well as malaria, mosquitoes can transmit viruses including dengue fever, yellow fever, West Nile virus and chikungunya. Luckily for the UK, the species that carries most of these diseases, <em>Aedes egypti</em>, doesn’t live here, but it is increasing its range. It recolonised Madeira in 2004-2005 and <a href="http://ecdc.europa.eu/en/healthtopics/vectors/mosquitoes/Pages/aedes-aegypti.aspx#sthash.GEglDxuy.dpuf">there are concerns</a> that it could be transported to western European countries.</p>
<h2>Malaria in the past</h2>
<p>There are very few recent cases of malaria transmission in the UK, although <a href="http://pmj.bmj.com/content/80/949/663.full">there is evidence</a> for the disease’s presence from the 14th to the 17th centuries. Shakespeare even mentioned it in The Tempest. Malaria in the UK <a href="http://e-m-b.org/sites/e-m-b.org/files/European_Mosquito_Bulletin_Publications811/EMB01/EMB01_05.pdf">virtually died out</a> by the end of the 19th century due to a combination of marsh drainage, use of quinine and better sanitation. </p>
<p>Aside from this, the absence of malaria in Western Europe is most likely due to its climate. Plasmodium needs a sustained high temperature to complete its reproduction in the mosquito. The lack of the species mainly involved in transmission of the disease is also crucial. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=264&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=264&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=264&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87914/original/image-20150709-10876-1j6nr9o.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Malaria free for how long?</span>
</figcaption>
</figure>
<p>However, the UK’s freedom from dangerous mosquitoes could be set to change. Firstly, with increased globalisation and faster transport, non-native species could be introduced in sufficient numbers to establish a breeding population.</p>
<p>Most insects are strongly “r-selected”, meaning they have evolved to produce large numbers of offspring but live relatively short lives. That means once a species has established itself in a location it can increase very rapidly. For example, Harlequin ladybirds spread over <a href="https://www.buglife.org.uk/bugs-and-habitats/harlequin-ladybird">most of southern Britain</a> in just 10 years, with a much slower breeding rate than mosquitoes.</p>
<p>Secondly, temperatures are predicted to increase due to climate change. A review published in <a href="http://bit.ly/1Hv1vtS">The Lancet Infectious Diseases</a> concludes that warmer conditions and more rainfall could provide the right conditions for disease carrying mosquitoes to arrive in the UK. Existing species such as the common <em>Culex pipiens</em>, could spread West Nile Virus here. Another virus-carrying species, <em>Culex modestus</em> has <a href="http://www.parasitesandvectors.com/content/5/1/32">already established colonies</a> in the Thames estuary.</p>
<h2>Tiger mosquitoes</h2>
<p>A further problem is the Asian tiger mosquito (<em>Aedes albopictus</em>), which spreads dengue fever and chikungunya. Both can be serious illnesses and have no effective treatment. This mosquito’s spread, especially in the United States, has been exacerbated by the international trade in used tyres, whose colour and structure provide ideal incubation pools for the species’ aquatic larvae.</p>
<p>Predictions based on a 2<sup>o</sup>C temperature rise – the <a href="https://theconversation.com/two-degrees-how-we-imagine-climate-change-18035">commonly agreed limit</a> before which “dangerous” climate change will kick in – could extend Tiger mosquitoes’ activity season by a month and its range by up to 30% by 2030. In the past 10 years insect-borne diseases have spread within Europe, including Greece (malaria) West Nile virus (Eastern Europe), Italy and France (chikungunya). This temperature rise could lead to <a href="http://press.thelancet.com/vectorbornedisease.pdf">outbreaks of chikungunya</a> in south-eastern England by the second half of the century.</p>
<p>So as the climate warms, mosquitoes in the UK may no longer be just a pest that gets worse during the occasional heatwave. They may become a widespread, constant and dangerous health threat.</p><img src="https://counter.theconversation.com/content/44397/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Terrell Nield does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The UK’s recent heatwave is perfect for mosquito breeding but something far more dangerous may be coming.Christopher Terrell Nield, Principal lecturer, bioscience, Nottingham Trent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/349062015-01-07T11:11:21Z2015-01-07T11:11:21ZExplainer: what’s the difference between an outbreak and an epidemic?<p>More than <a href="http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/case-counts.html">8,000 people</a> have died from Ebola in West Africa since February 2014 and it has spread beyond the three countries initially affected. So, it’s an epidemic, right? Or is it an outbreak? </p>
<p>What about H1N1? The 2009 pandemic infected people around the world. But, so did the SARS epidemic in 2003. What’s the difference between an epidemic and pandemic? What about diseases like malaria and Dengue? Dengue fever infects between <a href="http://www.who.int/mediacentre/factsheets/fs117/en/">50 and 100 million</a> people each year in countries all over the world. So that’s the same thing as a pandemic? Not quite. Maybe you’ve seen headlines about West Nile Virus, Chikungunya fever or Middle East Respiratory Syndrome. And what are emerging and reemerging diseases?</p>
<p>It’s time to brush up on the vocabulary that can help you understand just what infectious disease experts are trying to tell us. </p>
<h2>Outbreaks, epidemics and pandemics</h2>
<p>An <a href="http://www.who.int/topics/disease_outbreaks/en/">outbreak</a> is the sudden occurrence of a disease in a community, which has never experienced the disease before or when cases of that disease occur in numbers greater than expected in a defined area. The current <a href="https://www.mja.com.au/journal/2014/201/6/vulnerability-hysteria-and-fear-conquering-ebola-virus">Ebola scenario</a> in West Africa started as an outbreak, which initially affected three countries.</p>
<p>So what exactly is an epidemic? It is an occurrence of a group of illnesses of similar nature and derived from a common source, in excess of what would be normally expected in a community or region. A classic example of an epidemic would be Severe Acute Respiratory Syndrome (SARS). The epidemic killed about 774 people out of 8,098 that were infected. It started as an outbreak in Asia and then spread to <a href="http://www.cdc.gov/sars/about/fs-SARS.html">two dozen countries</a> and took the form of an epidemic. The same is true for Ebola, which is now being termed an <a href="http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/">epidemic</a>. </p>
<p>A pandemic on the other hand refers to a worldwide epidemic, which could have started off as outbreak, escalated to the level of an epidemic and eventually spread to a number of countries across continents. The 2009 flu pandemic is a good example. Between the period of April 2009 and August 2010, there were approximately 18,449 deaths in over <a href="http://www.who.int/csr/don/2010_08_06/en/">214 countries</a>. The flu virus (H1N1) probably originated in <a href="http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0430a2.htm">Mexico</a> and within two months, sustained human-to-human transmission in several countries on different continents was reported, prompting the WHO to announce the highest alert level (<a href="http://www.who.int/csr/disease/swineflu/frequently_asked_questions/levels_pandemic_alert/en/">phase 6, pandemic</a>) on <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3073629/">June 12, 2009</a>.</p>
<h2>Endemic diseases</h2>
<p>Some diseases can remain active in a given area for years and years. A disease is described as endemic when it is habitually present within a given geographic area. For example, Dengue, which is spread by mosquitoes, is endemic in more than <a href="http://www.who.int/mediacentre/factsheets/fs117/en/">100 countries</a>. So why isn’t dengue considered a pandemic yet? The point to consider here is that the dengue cases are not from a common source. Mosquitoes do not fly beyond a <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3342775/">few hundred meters</a>, so the cases in each country are from a different source. Rotavirus-induced infant diarrhea is another example of an endemic disease, which is rampant in developing <a href="http://www.histopathology-india.net/rota.htm">countries</a>. </p>
<h2>Emerging and reemerging diseases</h2>
<p>We also come across words like “emerging” and “re-emerging.” An <a href="http://www.who.int/topics/emerging_diseases/en/">emerging disease</a> is one that has appeared in a population for the first time or one which may have existed before, but is rapidly increasing in incidence. Examples of emerging infectious diseases are <a href="http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1003467">SARS, HIV and H1N1</a>. </p>
<p>Despite advances made in the field of medicine, global travel has added to the complexity of controlling infectious diseases. Both the 2003 SARS epidemic and the 2009 H1N1 pandemic were spread to a large extent due to air travel. </p>
<p>Chikungunya is another <a href="http://wwwnc.cdc.gov/eid/article/20/8/14-0333_article">viral disease</a> that is emerging in the Western Hemisphere. The first known cases in the Western Hemisphere occurred around October 2013 among residents of the French side of St. Martin in the Caribbean. WHO confirmed more than 31,000 probable and confirmed cases, which were not imported but indigenous in nature, from numerous other Caribbean islands as of <a href="http://wwwnc.cdc.gov/eid/article/20/8/14-0333_article">April 2014</a>. </p>
<p>Middle East Respiratory Syndrome (MERS) emerged around <a href="http://www.phac-aspc.gc.ca/phn-asp/2013/ncoronavirus-eng.php">April 2012</a> and has affected countries in the Middle East, Europe, Africa, Asia and North America, with 945 human cases, including 348 deaths as of <a href="http://www.phac-aspc.gc.ca/phn-asp/2013/ncoronavirus-eng.php">January 6, 2015</a>.</p>
<p><a href="http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1003467">Reemerging diseases</a> are those that have historically infected humans, but continue to appear in new locations or reappear after apparent control or elimination. Most of the reemerging disease agents appeared long ago and have survived and persisted in the environment. A classic example is the West Nile virus (WNV). It is thought that WNV arrived in the United States via an infected traveler, bird or mosquito, which entered America through air travel from the <a href="http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1003467">Middle East</a>. </p>
<h2>Why bother?</h2>
<p>Although people use terms like outbreak and epidemic interchangeably, it would only be fair to understand the definitive meaning behind each word. An outbreak can take the form of an epidemic and eventually a pandemic, but that does not entitle us to use these words incorrectly.</p><img src="https://counter.theconversation.com/content/34906/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arinjay Banerjee does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>More than 8,000 people have died from Ebola in West Africa since February 2014 and it has spread beyond the three countries initially affected. So, it’s an epidemic, right? Or is it an outbreak? What about…Arinjay Banerjee, PhD Candidate in Veterinary Microbiology, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/293112014-07-23T06:44:21Z2014-07-23T06:44:21ZWhy are emerging viruses here – and why now?<figure><img src="https://images.theconversation.com/files/54559/original/zjxqt6bk-1406037851.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Not malaria - guess again.</span> <span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Aedes_Albopictus.jpg">James Gathany/CDC</a></span></figcaption></figure><p>The US <a href="http://www.vox.com/2014/7/19/5916249/chikungunya-fever-virus-caribbean-florida-disease-symptoms-explained">is on the brink</a> of a new virus epidemic; a virus that wasn’t there ten years ago but which is now worrying officials. Chikungunya, which causes an incapacitating fever, is spread via Aedes mosquitoes and usually found across Africa and Eurasia. But it is now the most recent example of an emerging virus – viruses that are rapidly changing their geographic distribution and/or their incidence. </p>
<p>Other emerging viruses such as the Ebolaviruses – which go on to cause ebola haemorrhagic fever – and severe acute respiratory syndrome <a href="http://www.cdc.gov/sars/">coronavirus</a> (SARS-CoV), are less common while others like mumps virus, are re-emerging after a period of relative absence in the western hemisphere. These viruses arise, often unexpectedly, amid some level of mystery about where they come from and why they are spreading. Their origins are more complex than they might appear. </p>
<h2>Arboviruses affected by climate</h2>
<p>Viruses like chikungunya that are spread by arthropods (insects and arachnids, like ticks) are known as arboviruses (from arthropod borne)
and are affected by climate change and global warming, which directly facilitates their emergence. Global warming affects the distribution of arthropods, which act as vectors for the virus and increase the capacity for the viruses to grow within them. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=481&fit=crop&dpr=1 600w, https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=481&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=481&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=605&fit=crop&dpr=1 754w, https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=605&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/54565/original/86nzp8t9-1406039155.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=605&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Colour coding.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/ajc1/1003382495/sizes/o/">AJC1</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>An outbreak of Bluetongue virus – an infection of sheep and cattle that is spread by Culicoides midges – <a href="http://wwwnc.cdc.gov/eid/article/15/3/pdfs/08-1210.pdf">began in northern Europe</a> in 2006, where it had never been seen before, and infected more animals than previously recorded. </p>
<p>Now, Chikungunya virus would appear set to spread across the US, much as West Nile virus did after it appeared in New York in 1999 – and which <a href="http://www.nydailynews.com/new-york/queens/west-nile-virus-discovered-douglaston-college-point-article-1.1868081">is still appearing</a>. But not all emerging viruses are as predictable as the arboviruses.</p>
<h2>Zoonotic viruses</h2>
<p>A significant proportion of emerging viruses are zoonotic viruses, which spread from animals. These viruses are the most unpredictable, meaning that interaction between animals and humans is critical to their “spillover” into humans. The domestication of livestock has allowed multiple species – each with their own viruses - to come into close contact, which has created the right conditions for zoonosis. </p>
<p><a href="https://theconversation.com/avian-flu-may-have-moved-between-humans-but-were-still-far-from-a-pandemic-13920">Poultry</a> and pigs are well known for a generation of new novel influenza viruses. However, it was also pig farms that ultimately resulted in the first cases of <a href="http://www.ncbi.nlm.nih.gov/pubmed/12637075">Nipah virus</a> in Malaysia in 1999. Though harboured by flying foxes, the virus spread to pigs and then to humans <a href="http://www.cdc.gov/mmwr/preview/mmwrhtml/00057012.htm">causing around 100 deaths</a>. </p>
<p>Human encroachment into new environments and the disruption of wildlife can also lead to humans being exposed to animals and their viruses. Outbreaks of ebolavirus haemorrhagic fever in African villages <a href="http://www.foodsafetynews.com/2012/09/deadly-african-ebola-virus-linked-to-bushmeat/#.U85xuaZb--8">are often associated</a> with the bushmeat trade.</p>
<h2>A reproductive number</h2>
<p>The myriad examples of virus emergence can be understood using the concept of <a href="http://web.stanford.edu/%7Ejhj1/teachingdocs/Jones-on-R0.pdf">the basic reproductive number</a>, otherwise known as R0, which is a measure of the average number of new infections a virus produced from one single infection. An R0 of one means that an average of one new infection will arise from another, while a virus with an R0 of more than one will spread efficiently throughout a population. If a virus has an R0 of less than one it may eventually die out, as it fails to generate enough new infections over time – unless it is continuously re-introduced. </p>
<p>Processes that influence this number affect emergence. So while emerging viruses with an R0 of less than one may fail to efficiently infect and transmit within a new population, climate change and human behaviour could influence a virus’ R0 score in a given geographical area. Also important are virus-host interactions at the level of cells, which is a process governed by evolution. What makes viruses like chikungunya so worrying is that they require no further evolution to infect humans.</p>
<h2>A suitable host</h2>
<p>Viruses, as obligate, intracellular parasites that need hosts to spread, are composed of a protein or lipid coat that protects the viral genome, which encodes the instructions to make the viral proteins needed for infection. These proteins must allow entry of the virus into the host cell; make new copies of themselves; spread to more cells and evade your immune system. Differences in the efficiencies of these steps can all influence R0. </p>
<p>A virus’ genome can influence the fit between viral and host proteins; a virus with a better fit may be selected for and increase in frequency – which we can see as emergence.</p>
<p>Some viruses adapt and transmit easily, such as SARS-CoV and influenza (until we put a stop to them), while others fail to change their transmission, such as ebolavirus <a href="https://theconversation.com/camels-likely-suspects-behind-mers-but-mysteries-remain-16918">and the recent</a> Middle-eastern respiratory syndrome (MERS)-CoV. </p>
<p>A constant worry is that an emerging virus may evolve to transmit efficiently within the human population but we do have means to prevent virus emergence. Intense monitoring of changes in virus distribution and novel human/animal infections lies at the heart of our strategy to combat emerging viruses. </p>
<p>For chikungunya and its relatives, targeting the mosquitoes that help it to spread and reducing the burden of climate change on at-risk areas may contain spread into new regions. The development of effective antiviral drugs and vaccines could also secure virus control. However, a challenge lies in predicting which viruses are most important and difficult in a global arena of continuing complexity and uncertainty. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/54568/original/4ks6vh8s-1406039872.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">HIV: firmly established.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:HIV-budding-Color.jpg"> C. Goldsmith/CDC</a></span>
</figcaption>
</figure>
<p>The reality is that we have lived through this before with HIV/Aids and the spectre of once emerging but now-established viruses. This should continue to pique our interest in dealing with new ones that appear. </p><img src="https://counter.theconversation.com/content/29311/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The US is on the brink of a new virus epidemic; a virus that wasn’t there ten years ago but which is now worrying officials. Chikungunya, which causes an incapacitating fever, is spread via Aedes mosquitoes…Andrew Shaw, Postdoctoral Research Scientist, University of GlasgowConnor G G Bamford, Post-doctoral Research Assistant, University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/89352012-08-21T04:50:22Z2012-08-21T04:50:22ZExplainer: West Nile virus outbreak in the United States<figure><img src="https://images.theconversation.com/files/14460/original/zrm8jhrt-1345513170.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">West Nile virus is responsible for a significant number of bird deaths in the United States.</span> <span class="attribution"><span class="source">Ed Gaillard</span></span></figcaption></figure><p>A state of emergency has been declared in Dallas, Texas as local authorities battle an outbreak of the deadly West Nile virus. The state is on track to report record numbers of the mosquito-borne disease and local authorities have commenced broad-scale mosquito control. </p>
<p>But concerns have been raised by local communities upset at the prospect of aerial spraying due to perceptions of the potential health and environmental impacts of the insecticides.</p>
<h2>What is West Nile virus?</h2>
<p>West Nile virus is spread by mosquitoes and causes a potentially deadly illness. Only about one in five infected people get sick but for a small number of those (particularly those over 50), the infection can be fatal. For people with milder infections, symptoms include fever, headache, body aches, nausea, vomiting, swollen lymph glands or a skin rash.</p>
<p>Since the virus was first detected in North America in 1999, it has spread across the continent and had a significant impact on the health of both people and wildlife. It’s responsible for an estimated <a href="http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8598448&fulltextType=BT&fileId=S0950268812001070">800,000 cases</a> of infections and a significant number of <a href="http://www.nature.com/nature/journal/v447/n7145/abs/nature05829.html">bird deaths</a>.</p>
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<figcaption>
<span class="caption">Map shows the distribution of West Nile virus activity in the United States in 2012 (to 14 August) by state.</span>
<span class="attribution"><span class="source">CDC/USGS http://www.cdc.gov/ncidod/dvbid/westnile/Mapsactivity/surv&control12MapsAnybyState.htm</span></span>
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<h2>The current outbreak</h2>
<p>According to the US <a href="http://www.cdc.gov/ncidod/dvbid/westnile/index.htm">Centers for Disease Control and Prevention</a> a total of 693 cases of West Nile virus disease, including 26 deaths, have been reported so far this year. An unseasonably warm winter, followed by a wet spring and hot summer, have created perfect conditions for an epidemic.</p>
<p>Texas has been hardest hit. The <a href="http://www.dshs.state.tx.us/idcu/disease/arboviral/westNile/">Texas Department of State Health Services</a> is reporting a total of 552 cases, including 21 deaths for the year to date.</p>
<p>Debate surrounds the factors contributing to the current outbreak. Local environmental conditions have no doubt played a role in influencing the abundance of mosquito populations, but it isn’t just the number of mosquitoes that’s important. The type and behaviour of mosquitoes, as well as the local wildlife that carry the virus, are key factors.</p>
<p>Mosquitoes generally need to bite an infected animal before they can pass the virus on to a person. Extensive studies in North America show that birds are the main reservoirs of the West Nile virus. Most importantly, the birds that play a role in spreading West Nile virus are generally thought to be <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2958552/">passerine species</a> found in urban environments living close to people.</p>
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<img alt="" src="https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/14459/original/3pcc8w65-1345513025.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The spread of West Nile virus.</span>
<span class="attribution"><span class="source">AJ Cann</span></span>
</figcaption>
</figure>
<p>The mosquitoes responsible for spreading West Nile virus belong to the <em>Culex</em> genus. These mosquitoes are commonly found in urban environments, particularly heavily polluted habitats, such as drains and storm water systems. </p>
<p>The mosquitoes generally prefer to bite birds and play an important role in <a href="http://www.sciencedirect.com/science/article/pii/S1567134811002929">spreading pathogens from birds to humans</a>. <a href="http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0040082">Studies</a> also show that intense outbreaks occur as mosquitoes’ feeding habits shift from birds to humans in late summer. This may go some way to explaining the timing of the current outbreak.</p>
<p>It’s also important to consider the role of local bird populations. <a href="http://www.springerlink.com/content/g05286p02165j5m8/">Studies</a> show that a lower diversity of local bird species can increase the risks of West Nile infection in humans. </p>
<p>Has this year’s weather favoured those birds more likely to be carrying the virus? Are there more infected birds as well as more mosquitoes? Understanding outbreaks of West Nile virus requires more information on a range of factors, not just temperature but also on rainfall, and how many mosquitoes are about.</p>
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<img alt="" src="https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/14450/original/jt4g5cyy-1345508220.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mosquitoes in the Culex pipiens complex play an important role in outbreaks of West Nile virus.</span>
<span class="attribution"><span class="source">Stephen Doggett, Medical Entomology</span></span>
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</figure>
<h2>How to stop it</h2>
<p>There’s no vaccine for West Nile virus so preventing disease requires a reduction in the mosquito population or a change in human behaviour. During disease outbreaks, infected adult mosquitoes flying about need to be knocked down. </p>
<p>A balance between public and environmental risk has to be made when the decision is made to spray for mosquitoes. Despite the seriousness of the outbreak, <a href="http://www.change.org/petitions/dallas-stop-the-spray-combat-mosquitoes-the-intelligent-way">concerns about the possible health and environmental risks</a> associated with mosquito control have been raised in Texas.</p>
<p>The products most commonly used against adult mosquitoes are synthetic pyrethroids. These insecticides are applied at ultra low volumes, often by aircraft or vehicle-mounted sprayers. Although there’s no evidence that spraying these insecticides directly impacts human or animal health, other insects can be killed if exposed to the spray. These non-target impacts can be minimised by spraying at dusk when mosquitoes are most active.</p>
<p>Even with aerial spraying, individuals should still take steps to prevent mosquito bites. The first line of defence is using insect repellents. There’s a range of <a href="http://www.cdc.gov/ncidod/dvbid/westnile/RepellentUpdates.htm">effective products and formulations of insect repellents available</a> and, when used correctly, they <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2915.2012.01020.x/full">can prevent disease</a>.</p>
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<figcaption>
<span class="caption">The application of topical insect repellents can assist in preventing the spread of mosquito-borne disease.</span>
<span class="attribution"><span class="source">Medical Entomology, Westmead Hospital</span></span>
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<p>Outbreaks of West Nile virus, as the United States is currently experiencing, are a timely reminder of how difficult it can be to predict and prevent mosquito-borne disease. Complex environmental, biological and ecological factors are at play, and the education, attitude and behaviour of humans needs to be considered. There are gaps in our knowledge about appropriate surveillance and control strategies for preventing future outbreaks.</p><img src="https://counter.theconversation.com/content/8935/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The author has no potential conflicts of interest to disclose</span></em></p>A state of emergency has been declared in Dallas, Texas as local authorities battle an outbreak of the deadly West Nile virus. The state is on track to report record numbers of the mosquito-borne disease…Cameron Webb, Clinical Lecturer and Hospital Scientist, University of SydneyLicensed as Creative Commons – attribution, no derivatives.