tag:theconversation.com,2011:/id/topics/retroviruses-3884/articlesRetroviruses – The Conversation2022-10-18T18:03:18Ztag:theconversation.com,2011:article/1923222022-10-18T18:03:18Z2022-10-18T18:03:18ZHumans are 8% virus – how the ancient viral DNA in your genome plays a role in human disease and development<figure><img src="https://images.theconversation.com/files/489839/original/file-20221014-18-y4o10m.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2121%2C1412&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Pandemics over the course of evolution have led to the integration of viruses into our genome.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/three-dimensional-render-of-single-royalty-free-illustration/1249814587">Westend61via Getty Images</a></span></figcaption></figure><p>Remnants of ancient viral pandemics in the form of viral DNA sequences embedded in our genomes are still active in healthy people, according to <a href="http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001826">new research</a> my <a href="https://scholar.google.com/citations?hl=en&user=AZcPXsIAAAAJ">colleagues</a> <a href="https://scholar.google.com/citations?user=pyRxplAAAAAJ&hl=en">and I</a> recently published.</p>
<p>HERVs, or human endogenous retroviruses, make up around <a href="https://doi.org/10.1038/35057062">8% of the human genome</a>, left behind as a result of infections that humanity’s primate ancestors suffered millions of years ago. They became part of the human genome due to how they replicate. </p>
<p>Like modern HIV, these ancient <a href="https://doi.org/10.1099%2Fjgv.0.001712">retroviruses</a> had to insert their genetic material into their host’s genome to replicate. Usually this kind of viral genetic material isn’t passed down from generation to generation. But some ancient retroviruses gained the ability to <a href="https://doi.org/10.1038/s41579-019-0189-2">infect germ cells</a>, such as egg or sperm, that do pass their DNA down to future generations. By targeting germ cells, these retroviruses became incorporated into human ancestral genomes over the course of millions of years and may have implications for how researchers screen and test for diseases today.</p>
<h2>Active viral genes in the human genome</h2>
<p>Viruses insert their genomes into their hosts in the form of a <a href="https://www.verywellhealth.com/provirus-hiv-glossary-definition-48962">provirus</a>. There are around <a href="https://doi.org/10.1186/1742-4690-2-50">30 different kinds</a> of human endogenous retroviruses in people today, amounting to over 60,000 proviruses in the human genome. They demonstrate the long history of the many pandemics humanity has been subjected to over the course of evolution. Scientists think these viruses once widely infected the population, since they have become fixed in not only the human genome but also in <a href="https://doi.org/10.1371%2Fjournal.pone.0101195">chimpanzee</a>, <a href="https://doi.org/10.1073/pnas.1814203116">gorilla</a> and other primate genomes.</p>
<p>Research from <a href="https://gsbs.tufts.edu/facultyResearch/faculty/coffin-john/research">our lab</a> and others has demonstrated that HERV genes are active in diseased tissue, such as <a href="https://doi.org/10.1128/JVI.01258-17">tumors</a>, as well as during <a href="https://doi.org/10.1016%2Fj.csbj.2021.10.037">human embryonic development</a>. But how active HERV genes are in healthy tissue was still largely unknown.</p>
<p>To answer this question, our lab decided to focus on one group of HERVs known as HML-2. This group is the <a href="https://doi.org/10.1186/1742-4690-8-90">most recently active of the HERVs</a>, having gone extinct less than 5 million years ago. Even now, some of its proviruses within the human genome still retain the ability to make viral proteins. </p>
<p>We examined the genetic material in a <a href="https://www.gtexportal.org/home/">database</a> containing over 14,000 donated tissue samples from all across the body. We looked for sequences that matched each HML-2 provirus in the genome and found 37 different HML-2 proviruses that were still active. All 54 tissue samples we analyzed had some evidence of activity of one or more of these proviruses. Furthermore, each tissue sample also contained genetic material from at least one provirus that could still produce viral proteins.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FmX8au0xGlY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">HERVs have influenced humans in ways researchers are still figuring out.</span></figcaption>
</figure>
<h2>The role of HERVs in human health and disease</h2>
<p>The fact that thousands of pieces of ancient viruses still exist in the human genome and can even create protein has drawn a considerable amount of attention from researchers, particularly since related viruses still active today can cause <a href="https://doi.org/10.3390%2Fv2092000">breast cancer</a> and <a href="https://doi.org/10.1111%2Fj.1600-0684.2010.00412.x">AIDS-like disease</a> in animals.</p>
<p>Whether the genetic remnants of human endogenous retroviruses can cause disease in people is still under study. Researchers have spotted viruslike particles from HML-2 <a href="https://doi.org/10.1006/viro.1993.1487">in cancer cells</a>, and the presence of HERV genetic material in diseased tissue has been associated with conditions such as <a href="https://doi.org/10.3390%2Fmicroorganisms9081784">Lou Gehrig’s disease, or amyotrophic lateral sclerosis</a>, as well as <a href="https://doi.org/10.1007/s12035-018-1255-x">multiple sclerosis</a> and even <a href="https://doi.org/10.3389%2Ffpsyt.2015.00183">schizophrenia</a>.</p>
<p>Our study adds a new angle to this data by showing that HERV genes are present even in healthy tissue. This means that the presence of HERV RNA may not be enough to connect the virus to a disease. </p>
<p>Importantly, it also means that HERV genes or proteins may no longer be good targets for drugs. HERVs have been explored as a target for a number of potential drugs, including <a href="https://doi.org/10.1186/s12977-017-0347-4">antiretroviral medication</a>, <a href="https://doi.org/10.1093/jnci/djr540">antibodies for breast cancer</a> and <a href="https://doi.org/10.1158/1078-0432.ccr-14-3197">T-cell therapies for melanoma</a>. Treatments using HERV genes as a cancer biomarker will also need to take into account their activity in healthy tissue.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/CDA1ISk0rlI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A developing fetus shares a few commonalities with viruses.</span></figcaption>
</figure>
<p>On the other hand, our research also suggests that HERVs could even be beneficial to people. The most famous HERV embedded in human and animal genomes, <a href="https://doi.org/10.1016/j.placenta.2012.05.005">syncytin</a>, is a gene derived from an ancient retrovirus that plays an important role in the formation of the placenta. Pregnancy in all mammals is dependent on the virus-derived protein coded in this gene. </p>
<p>Similarly, <a href="https://doi.org/10.1038/382826a0">mice</a>, <a href="https://doi.org/10.1128%2FJVI.01267-13">cats</a> and <a href="https://doi.org/10.1128%2FJVI.01859-06">sheep</a> also found a way to use endogenous retroviruses to protect themselves against the original ancient virus that created them. While these embedded viral genes are unable to use their host’s machinery to create a full virus, enough of their damaged pieces circulate in the body to interfere with the replication cycle of their ancestral virus if the host encounters it. Scientists theorize that <a href="https://doi.org/10.7554/elife.22519">one HERV</a> may have played this protective role in people millions of years ago. Our study highlights a few more HERVs that could have been claimed or co-opted by the human body much more recently for this same purpose.</p>
<h2>Unknowns remain</h2>
<p>Our research reveals a level of HERV activity in the human body that was previously unknown, raising as many questions as it answered. </p>
<p>There is still much to learn about the ancient viruses that linger in the human genome, including whether their presence is beneficial and what mechanism drives their activity. Seeing if any of these genes are actually made into proteins will also be important.</p>
<p>Answering these questions could reveal previously unknown functions for these ancient viral genes and better help researchers understand how the human body reacts to evolution alongside these vestiges of ancient pandemics.</p><img src="https://counter.theconversation.com/content/192322/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aidan Burn receives funding from the National Cancer Institute. </span></em></p>Bits of viral genes incorporated into human DNA have been linked to cancer, ALS and schizophrenia. But many of these genes may not be harmful, and could even protect against infectious disease.Aidan Burn, PhD Candidate in Genetics, Tufts UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1346562020-04-06T03:26:57Z2020-04-06T03:26:57ZHow do viruses mutate and jump species? And why are ‘spillovers’ becoming more common?<figure><img src="https://images.theconversation.com/files/325549/original/file-20200406-178224-1xapi3e.jpg?ixlib=rb-1.1.0&rect=94%2C63%2C5170%2C3441&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/beautiful-malayan-tiger-female-walking-straight-593861213">Shutterstock</a></span></figcaption></figure><p>Viruses are little more than parasitic fragments of <a href="https://www.thoughtco.com/dna-versus-rna-608191">RNA or DNA</a>. Despite this, they are <a href="https://www.nature.com/articles/nature19094">astonishingly abundant</a> in number and <a href="https://www.biorxiv.org/content/10.1101/583997v2.abstract">genetic diversity</a>. We don’t know how many virus species there are, but there could be <a href="https://www.nytimes.com/2020/03/24/science/viruses-coranavirus-biology.html">trillions</a>. </p>
<p>Past viral epidemics have influenced the evolution of all life. In fact, about <a href="https://link.springer.com/article/10.1186/1742-4690-8-90">8% of the human genome</a> consists of retrovirus fragments. These genetic “fossils” are leftover from viral epidemics our ancestors survived. </p>
<p>COVID-19 reminds us of the devastating impact viruses can have, not only on humans, but also <a href="https://search.informit.com.au/documentSummary;dn=727884093581250;res=IELBus">animals</a> and <a href="https://link.springer.com/article/10.1007/s00705-014-2295-9">crops</a>. Now for the first time, the disease has been <a href="https://www.smh.com.au/world/north-america/tiger-tests-positive-for-coronavirus-at-new-york-s-bronx-zoo-20200406-p54hcq.html">confirmed in a tiger</a> at New York’s Bronx Zoo, believed to have been infected by an employee. Six other tigers and lions were also reported as “showing symptoms”.</p>
<p><a href="https://www.bbc.com/news/world-us-canada-52177586">According to the BBC</a>, conservation experts think COVID-19 could also threaten animals such as wild gorillas, chimps and orangutans.</p>
<p>While virologists are intensely interested in how viruses mutate and transmit between species – and understand this process to an extent – many gaps in knowledge remain. </p>
<h2>Skilled in their craft</h2>
<p>Most viruses are specialists. They establish long associations with preferred host species. In these relationships, the virus may not induce disease symptoms. In fact, the virus and host may <a href="https://science.sciencemag.org/content/315/5811/513">benefit each other in symbiosis</a>.</p>
<p>Occasionally, viruses will “emerge” or “spillover” from their original host to a new host. When this happens, the risk of disease increases. Most infectious diseases that affect <a href="https://www.nature.com/articles/nature23088">humans</a> and our food supply are the result of spillovers from wild organisms. </p>
<p>The new coronavirus (SARS-CoV-2) that emerged from Wuhan in November isn’t actually “new”. The virus evolved over a long period, probably <a href="https://jvi.asm.org/content/87/12/7039.short">millions of years</a>, in other species where it still exists. We know the virus has close relatives in Chinese rufous horseshoe bats, intermediate horseshoe bats, and <a href="https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwaa036/5775463">pangolins</a> - which are <a href="https://www.nytimes.com/2020/03/05/opinion/coronavirus-china-pangolins.html">considered a delicacy in China</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/325554/original/file-20200406-74279-1c1dgns.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">Smuggled pangolins are killed for their scales to be used in traditional Chinese medicine. They are suspected to be the world’s most-trafficked mammal, apart from humans.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/java-pangolin-manis-javanica-on-green-1647891502">Shutterstock</a></span>
</figcaption>
</figure>
<p>Past coronaviruses, including the severe acute respiratory syndrome coronavirus (SARS-CoV), have jumped from bats to humans via an intermediary mammal. Some experts propose <a href="https://www.nature.com/articles/s41586-020-2169-0_reference.pdf">Malayan pangolins provided SARS-CoV-2 this link</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/coronavirus-origins-genome-analysis-suggests-two-viruses-may-have-combined-134059">Coronavirus origins: genome analysis suggests two viruses may have combined</a>
</strong>
</em>
</p>
<hr>
<p>Although the original host of the SARS-CoV-2 virus hasn’t been identified, we needn’t be surprised if the creature <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4012789/">appears perfectly healthy</a>. Many other coronaviruses <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/jmv.25681?casa_token=S5GVE2lp4o8AAAAA%3AJIax_f8vaYc0ujDW5Q9Jm8a3UleP-wa8wjFt9xDPkh642hFNKRM_nJbthkoajt1qpWePwAdlAP0HwgA">exist naturally</a> in wild mammal and bird populations around the world.</p>
<h2>Where do they keep coming from?</h2>
<p>Human activity drives the emergence of new pathogenic (disease-causing) viruses. As we push back the boundaries of the last wild places on Earth – felling the bush for farms and plantations – viruses from wildlife interact with <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev-virology-092818-015536">crops</a>, <a href="https://www.mdpi.com/1999-4915/9/5/103">farm animals</a> and people. </p>
<p>Species that evolved separately are now mixing. Global markets allow the free trade of live animals (including their eggs, semen and meat), vegetables, <a href="https://link.springer.com/article/10.1007/s00705-019-04317-7">flowers</a>, <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4136854/">bulbs and seeds</a> – and viruses come along for the ride. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-new-coronavirus-emerged-from-the-global-wildlife-trade-and-may-be-devastating-enough-to-end-it-133333">The new coronavirus emerged from the global wildlife trade – and may be devastating enough to end it</a>
</strong>
</em>
</p>
<hr>
<p>Humans are also warming the climate. This allows certain species to <a href="https://royalsocietypublishing.org/doi/full/10.1098/rstb.2010.0037">expand their geographical range</a> into zones that were previously too cold to inhabit. As a result, many viruses are meeting new hosts for the first time.</p>
<h2>How do they make the jump?</h2>
<p>Virus spillover is a complex process and not fully understood. In nature, most viruses are confined to particular hosts because of specific protein “lock and key” interactions. These are needed for successful replication, movement within the host, and transmission between hosts. </p>
<p>For a virus to infect a new host, some or all protein “keys” may need to be modified. These modifications, called “mutations”, can occur within the old host, the new one, or both. </p>
<p>For instance, a virus can jump from host A to host B, but it won’t replicate well or transmit between individuals unless multiple protein keys mutate either simultaneously, or consecutively. The low probability of this happening makes spillovers uncommon. </p>
<p>To better understand how spillovers occur, imagine a virus is a short story printed on a piece of paper. The story describes:</p>
<ol>
<li>how to live in a specific cell type, inside a specific host</li>
<li>how to move to the cell next door</li>
<li>how to transmit to a new individual of the <em>same</em> species.</li>
</ol>
<p>The short story also has instructions on how to make a virus photocopying machine. This machine, an enzyme called a <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/polymerase">polymerase</a>, is supposed to churn out endless identical copies of the story. However, the polymerase occasionally makes mistakes. </p>
<p>It may miss a word, or add a new word or phrase to the story, subtly changing it. These changed virus stories are called “mutants”. Very occasionally, a mutant story will describe how the virus can live inside a totally new host species. If the mutant and this new host meet, a spillover can happen.</p>
<p>We can’t predict virus spillovers to humans, so developing vaccines preemptively isn’t an option. There has been ongoing discussions of a “<a href="https://www.nature.com/articles/d41586-019-02751-w">universal flu vaccine</a>” which would provide immunity against all influenza virus mutants. <a href="https://www.sciencealert.com/a-potential-universal-flu-vaccine-just-passed-its-fourth-clinical-trial">But so far</a> this hasn’t been possible.</p>
<h2>Let wildlife be wildlife</h2>
<p>Despite how many viruses exist, relatively few threaten us, and the plants and animals we rely on. </p>
<p>Nonetheless, some creatures are especially dangerous on this front. For instance, coronaviruses, Ebola and <a href="https://www.who.int/health-topics/marburg-virus-disease/">Marburg viruses</a>, <a href="https://www.nature.com/articles/nrmicro1323">Hendra and Nipah viruses</a>, <a href="https://www.health.nsw.gov.au/infectious/factsheets/pages/rabies-australian-bat-lyssavirus-infection.aspx">rabies-like lyssaviruses</a>, and <a href="https://www.nature.com/articles/ncomms1796">mumps/measles-like paramyxoviruses</a> all originate from <a href="https://royalsocietypublishing.org/doi/full/10.1098/rspb.2014.2124">bats</a>.</p>
<p>Given the enormous number of viruses that exist, and our willingness to provide them global transport, future spillovers are inevitable. We can reduce the chances of this by practising better virus surveillance in hospitals and on farms. </p>
<p>We should also recognise wildlife, not only for its intrinsic value, but as a potential source of disease-causing viruses. So let’s maintain a “social distance” and leave wildlife in the wild.</p><img src="https://counter.theconversation.com/content/134656/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steve Wylie is a study group chair with the International Committee on Taxonomy of Viruses. </span></em></p>A four-year-old female Malayan tiger has tested positive for COVID-19, with six other tigers and lions showing symptoms. It’s the first known case of a ‘wild’ animal catching the disease.Steve Wylie, Adjunct Associate Professor, Murdoch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1248962019-10-10T19:02:23Z2019-10-10T19:02:23ZA virus is attacking koalas’ genes. But their DNA is fighting back<p>A virus that infects koalas is steadily integrating itself into their DNA, ensuring that it is passed down from generation to generation. But the koala genome is defending itself, revealing that DNA has its own immune system to shut down invaders.</p>
<p>The virus, called koala retrovirus (KoRV), is linked to weakened immunity, cancer, and chlamydia infection in koalas. All retroviruses hijack the DNA in some cells of their host’s body, but not all of them manage to be transmitted to the host’s offspring.</p>
<h2>Your DNA is 8% virus</h2>
<p>Over the millions of years of evolutionary history, retroviruses have at one time or another made their way into the genomes of all species of vertebrates that we have studied. </p>
<p>We know about these ancient infections because retroviruses sometimes infect the animal’s sperm or egg cells, which means the virus incorporates its own DNA sequences into the genome that is passed from generation to generation. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/an-ancient-retrovirus-has-been-found-in-human-dna-and-it-might-still-be-active-56844">An ancient retrovirus has been found in human DNA – and it might still be active</a>
</strong>
</em>
</p>
<hr>
<p>These viral sequences can contribute to disease, but have also been “co-opted” by the host animals for processes that are essential to normal development. As much as 8% of the human genome is made up of the remnants of infectious viruses.</p>
<p>While we know that retroviruses have frequently appeared during evolutionary history, we don’t know much about how retroviral sequences infiltrate sperm and egg cells, or how these cells react. </p>
<h2>Catching a retrovirus in the act</h2>
<p>Almost all known retrovirus genome invasions happened millions of years ago. However, KoRV is a recently identified exception. The virus spreads between individuals, but is also infecting sperm and egg cells, so many koalas are born with this pathogen as part of their genome. </p>
<p>My colleagues and I at the University of Queensland are collaborating with scientists from the University of Massachusetts Medical School to analyse how koala sperm and egg cells respond to KoRV-A infection. </p>
<p>Our findings, <a href="https://www.cell.com/cell/fulltext/S0092-8674(19)31008-6">published today in Cell</a>, suggest these cells mount a novel “innate genome immune response” to viral infection, which may help control the spread of infectious KoRV. </p>
<p>Within this project, the team analysed DNA and RNA from different tissue samples from deceased wild koalas from South East Queensland. (Like DNA, RNA also contains genetic information about the koalas – but it is also what KoRV’s own genome is made of.)</p>
<p>The team specifically looked for short sequences of RNA, between 23 and 35 nucleotides long, known as PIWI Interacting RNAs (piRNAs). Clusters of piRNA sequences are retained within the genome and serve as a kind of memory bank of undesirable sequences – signatures of invading viruses – to be targeted.</p>
<h2>An immune system for the genome</h2>
<p>Based on our new findings, we suggest that there is a specialised immune system to defend against retroviral genome invasion. Like the ordinary immune system, this one includes an innate response – a sort of general-purpose defence against attackers – and an adaptive response, which learns to recognise specific pathogens and take them down.</p>
<p>At the early stages of egg or sperm infection, the altered DNA sequence results in a “molecular pattern” that is recognised by an innate genome immune system, which stops the activity of the virus and starts producing signature piRNA sequences to recognise the invader.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/koalas-sniff-out-juicy-leaves-and-break-down-eucalypt-toxins-its-in-their-genome-99203">Koalas sniff out juicy leaves and break down eucalypt toxins – it's in their genome</a>
</strong>
</em>
</p>
<hr>
<p>The innate immune response works until a memory of the genome invader is created and a sequence-specific adaptive response kicks in.</p>
<p>We propose a framework through which a sequence from an invading retrovirus can first have its genes “silenced”, and then through targeted processes it eventually becomes an integral part of the host genome. </p>
<p>This “genome immune system” changes our understanding of what shapes the genomes of all animals. No more can we view the genome as a defenceless entity governed purely by natural selection – it fights back.</p><img src="https://counter.theconversation.com/content/124896/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Keith Chappell receives funding from the Australian Research Council. </span></em></p>Koala retrovirus is a menace to koalas, but by watching it at work scientists are finding out how the genome defends itselfKeith Chappell, Senior Research Fellow, School of Chemistry and Molecular Biosciences, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/568442016-04-01T13:30:47Z2016-04-01T13:30:47ZAn ancient retrovirus has been found in human DNA – and it might still be active<figure><img src="https://images.theconversation.com/files/117099/original/image-20160401-6816-1quti7o.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">vitstudio/shutterstock.com</span></span></figcaption></figure><p>Striking evidence has emerged that an ancient virus previously known only from fossil evidence has persistently infected some humans at very low levels for hundreds of thousands or even millions of years. This ancient retrovirus is a kind of living fossil, and the discovery of an intact copy of it within the human genome poses questions as to how it has survived, and suggests <a href="http://www.ncbi.nlm.nih.gov/pubmed/22565131">others from the distant evolutionary past</a> may lie dormant in the DNA of many species. </p>
<p>A retrovirus replicates by inserting its genome into that of an infected cell. Occasionally, retroviruses infect germ line cells – those found in eggs and sperm – and if these cells survive and go on to create a new organism, that new organism will contain the retrovirus as an inherent part of its genome. In this way the genomes of many mammals, birds and other vertebrates have accumulated many DNA sequences derived from retroviruses, known as <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187282/">endogenous retroviruses</a> (ERVs). About 8% of the human genome is comprised of ERVs, for example. </p>
<p>The vast majority of these sequences are genomic fossils in an advanced state of decay, and incapable of producing any sort of infectious particles. Intriguingly, however, some ERVs have been co-opted to perform physiological functions within the host organism, <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4207369/">for example to provide immunity</a>. These domesticated virus sequences, though functional, have effectively become part of the host’s genome. They cannot produce infectious virus particles either, having generally lost the genetic equipment required to do so.</p>
<p>Nevertheless, there are a small proportion of ERV sequences that can make infectious particles, and these show that <a href="https://genomebiology.biomedcentral.com/articles/10.1186/gb-2006-7-11-241">the genomes of host species can be colonised by infectious retroviruses</a>. This process is poorly understood, but <a href="http://www.pnas.org/content/early/2016/03/16/1602336113.abstract">recent research</a> has shown the almost unbelievable stealth with which it can occur, so that the most modern and powerful techniques are required to detect it.</p>
<h2>The ‘Loch Ness Monster’ of the human genome</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=810&fit=crop&dpr=1 600w, https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=810&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=810&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1018&fit=crop&dpr=1 754w, https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1018&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/117096/original/image-20160401-6820-1dfjfhp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1018&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">All sorts of DNA lurks within the human genome.</span>
<span class="attribution"><span class="source">Promotive/shutterstock.com</span></span>
</figcaption>
</figure>
<p>Advances in whole genome sequencing have revealed a <a href="http://www.pnas.org/content/110/50/20146.abstract">huge diversity of ERVs in the genomes of vertebrates</a> with considerable difference between species. Many are extremely ancient, while more recent ERVs are more intact and less degraded by mutation. In <a href="http://www.microbe.tv/twiv/twiv-218-monkeys-turning-valves-and-pushing-buttons/">some species such as mice</a>, the genome contains many ERVs capable of producing infectious viruses, but almost all ERVs in humans (known as HERVs) appear to be non-functional remnants of extinct retroviruses. The only exception is one group, called <a href="http://www.ncbi.nlm.nih.gov/pubmed/8797733">HERV-K</a>, which is potentially capable of replication despite being many millions of years old.</p>
<p><a href="http://www.pnas.org/content/101/14/4894.long">Previous studies</a> of HERV-K sequences in the human genome have indicated that it has been <a href="http://phenomena.nationalgeographic.com/2013/05/10/the-lurker-how-a-virus-hid-in-our-genome-for-six-million-years/">recently active in humans</a>, and that it could even still circulate through infection. This recent study’s co-authors, Julia Wildschutte and Zach Williams, working in the <a href="http://sackler.tufts.edu/Faculty-and-Research/Faculty-Research-Pages/John-Coffin">laboratory of John Coffin</a> at <a href="https://www.tufts.edu/">Tufts University</a>, searched for evidence of HERV-K using data from the <a href="http://www.1000genomes.org/">1000 Genomes Project</a> and the <a href="http://www.hagsc.org/hgdp/">Human Genome Diversity Project</a>. The team developed approaches that allowed them to dig exceptionally deep into these catalogues and establish that the human genome contains a total of 36 unique HERV-K copies not present in the standard, <a href="http://hgdownload.cse.ucsc.edu/goldenpath/hg38/chromosomes/">reference human genome sequence</a> – including 19 new discoveries. </p>
<p>Most intriguingly of all, one of these new discoveries was an intact virus without any of the mutations that would be expected to degrade its function. The discovery of an intact virus lurking in the human population strengthens the possibility that this HERV-K retrovirus has remained “alive” within humans up until relatively recently, and could still be circulating somewhere even today.</p>
<h2>Future directions</h2>
<p>Many questions remain: is HERV-K really still active in humans? Is it lying dormant, poised to re-emerge as the agent of an infectious epidemic? Or are the signs of recent HERV-K activity really just the death throes of an ancient retrovirus as it drifts slowly but surely toward extinction? </p>
<p>It may be that by existing in a near-dormant state with only very low levels of activity, HERV-K has been able to evade the effects of mutations that would have inactivated it. Alternatively, there might be circumstances in which humans in some way gained a survival advantage that led to the presence of HERV-K in human DNA being selected for through evolutionary processes.</p>
<p>These hypotheses can be investigated to some extent because <a href="http://www.newyorker.com/magazine/2007/12/03/darwins-surprise">extinct retroviruses can be resurrected</a> from DNA remnants and their <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2519637/">biological properties analysed</a>. Studying how ancient viruses were extinguished by their host species can provide clues to strategies we might use to help fight the viruses that threaten us today.</p><img src="https://counter.theconversation.com/content/56844/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Gifford 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>How has a retrovirus survived intact within the human genome for millennia, and how has it affected us?Robert Gifford, Senior Research Fellow, University of GlasgowLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/496952016-03-31T10:24:47Z2016-03-31T10:24:47ZKnow your bugs – a closer look at viruses, bacteria and parasites<p>“<a href="https://newsinhealth.nih.gov/issue/feb2014/feature1">Stop the spread of superbugs</a>,” “<a href="http://www.cbsnews.com/pictures/15-superbugs-and-other-scary-diseases/">15 superbugs and other scary diseases</a>” and “<a href="http://www.cbc.ca/news/canada/superbug-bacteria-found-in-tested-hotel-rooms-1.1219281">Superbug bacteria found in tested hotel rooms</a>” are headlines we often read or hear about. But what do we mean when we say “bugs”? </p>
<p>The term is used to describe viruses, bacteria and parasites. While they can all make us sick, they do it in different ways. So what is the difference between these pathogens, and how dangerous are they? </p>
<p>Let’s start with viruses, the smallest of the three. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111038/original/image-20160210-12149-j2d08q.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">Electron microscope image of rabies virus (Rabdoviridae).</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/sanofi-pasteur/5279807113/in/photolist-93yoH8-pCYRsM-oKz53c-o6ranA-8U82Vv-rohGPk-wtWMT6-kWi25F-oiHjKy-7GSFFk-bNAUPK-bpyM7X-dSvvXv-7GSFTk-4DQVxT-sbNfYH-bpyMat-bpyMaa-7GWBWq-nghJ9j-nyjgrt-nwxrTZ-bpyM9K-wVxcFL-nghcM4-nxzwDE-nghnG6-nghrSZ-nxwcbq-nxN7k3-nxMfwB-nghFJ7-nK4fyk-nHf6y7-nKue2q-tASVX1-7GSFSH-7GSFUn-7GWBYW-nxkBiq">Sanofi Pasteur/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Viruses – from the common cold to Ebola</h2>
<p>Viruses have been around for a really, really long time. They predate us and could even be our <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3512416/">oldest ancestors</a>.</p>
<p>Viruses have helped build genomes of all species, including humans. Our genome is made up of 50 percent retroelements – the DNA from <a href="http://std.about.com/od/glossary/g/What-Is-A-Retrovirus.htm">retroviruses</a>. And viruses might have paved the way for several DNA <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3512416/">replication enzymes</a>, which are essential for a cell to divide and grow.</p>
<p>Viruses are capable of causing infections in humans and animals – and some viruses can even jump from one to the other. </p>
<p>Viruses have two phases of life. Outside a cell, they are nonliving and are called virion particles. Once inside a cell they use the cellular machinery to their advantage to replicate and <a href="https://theconversation.com/explainer-what-is-a-virus-22902">multiply</a>. Some scientists may argue that viruses are alive when inside a cell. </p>
<p>Some viruses, like the common cold, can make us sick, but don’t do lasting harm. But others are known to cause lethal disease in humans and animals. A pandemic strain of influenza can severely infect a large number of people in a very short time. There were an estimated 201, 200 respiratory deaths with an additional 83,300 cardiovascular deaths globally during the <a href="http://www.thelancet.com/journals/laninf/article/PIIS1473-3099(12)70121-4/abstract">2009 influenza (H1N1) pandemic</a>.</p>
<p>While we are exposed to virus particles every day, we don’t always fall sick because the immune system can handle most of them. We get sick when we encounter a new virus for the first time or in sufficient quantity. This is why it is recommended to get a flu shot every year. The circulating strain of influenza may vary each year, and immunity from a previous infection or vaccine might not protect us in the event of exposure to a different strain.</p>
<p>The ability to spread quickly and replicate rapidly makes some of these viruses dreaded entries on the list of pathogens, to an extent that some are even considered as potential weapons of <a href="http://www.ncbi.nlm.nih.gov/pubmed/12074486">mass destruction</a>. There are also viruses that kill slowly over time. A classic example is the rabies virus. It has a <a href="http://www.who.int/mediacentre/factsheets/fs099/en/">long incubation period</a> (1-3 months) and is vaccine-preventable, but once the symptoms set in, the individual is almost certain to die. </p>
<p>Vaccines are the best way to protect ourselves from viruses. Vaccines <a href="http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/prinvac.pdf">prime</a> the immune response, allowing our bodies to respond to an actual infection more efficiently. <a href="http://www.phac-aspc.gc.ca/im/vpd-mev/index-eng.php">Vaccines</a> have reduced the disease burden for several otherwise lethal viruses such as measles, rubella, influenza and smallpox. Beyond that, washing hands and covering noses while sneezing are practices that can keep some of these viruses at bay.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=567&fit=crop&dpr=1 754w, https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=567&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/111039/original/image-20160210-12185-1q0ei34.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=567&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Immunohistochemical detection of Helicobacter histopatholgy.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3AImmunohistochemical_detection_of_Helicobacter_(1)_histopatholgy.jpg">KGH via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Bacteria – toxin-producing invaders</h2>
<p>Some bacteria are good for you, offering protection against pathogens and aiding with digestion in the gut. But some aren’t so beneficial or benign. </p>
<p>Some are specialized to cause disease such as <a href="http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/staphylococcus-aureus-eng.php">Staphylococcal infection</a> (<em>Staphylococcus aureus</em>), <a href="http://www.health.gov.on.ca/en/public/publications/disease/botulism.aspx">botulism</a> (<em>Clostridium botulinum</em>), gonorrhea (<em>Neisseria gonorrhoeae</em>), gastric ulcer (<em>Helicobacter pylori</em>), diphtheria (<em>Corynebacterium diptheriae</em>) and bubonic plague (<em>Yersinia pestis</em>).</p>
<p>They can produce <a href="http://www.ncbi.nlm.nih.gov/books/NBK8526/">toxins</a>, invade cells or the bloodstream, or compete with the host for shared nutrients – all of which can lead to illness. The right course of treatment can depend on how the bacteria is causing illness. </p>
<p>Take botulism, for instance. People get it when they eat food contaminated with toxins or bacterial spores from <em>C. botulinum</em>. If a person ingests the toxin, he or she can develop <a href="http://www.cdc.gov/nczved/divisions/dfbmd/diseases/botulism/#symptoms">symptoms</a> within six to 36 hours. If the spore is ingested, it can take up to a week.</p>
<p><a href="http://emergency.cdc.gov/agent/botulism/hcpfacts.asp">Supportive</a> care is the primary therapeutic method, to prevent or relieve other possible complications and to maintain the health and breathing of the patient. Antibiotics treat infections by destroying the bacterium, but with <a href="http://www.phac-aspc.gc.ca/ep-mu/botulism-eng.php#b6">botulism</a>, the destruction of the bacterium can lead to the release of more toxins, causing severe illness. Doctors treat toxins by administering <a href="http://www.cdc.gov/nczved/divisions/dfbmd/diseases/botulism/">antitoxins or inducing vomiting</a>.</p>
<p>Today, thanks to the <a href="http://www.cbc.ca/news/health/antibiotic-resistance-colistin-1.3325942">misuse and overuse of antibiotics</a>, resistant bacteria is on the rise, and as of 2013, there were about <a href="http://www.who.int/mediacentre/factsheets/fs194/en/">480,000 </a>new cases of multidrug-resistant tuberculosis (MDR-TB).</p>
<p><a href="https://www.genomeweb.com/informatics/statistical-tool-helps-select-antibiotic-regimens-reverse-bacterial-drug-resistance">Cycling</a> between different antibiotics can reduce the risk of resistance. <a href="http://www.nature.com/news/antibiotic-alternatives-rev-up-bacterial-arms-race-1.17621">Alternatives</a>, such as bacteriophages (bacteria killing viruses) or enzymes that destroy the genome of resistant bacteria, are being developed. In fact, bacteriophages are widely used in Eastern <a href="http://www.bterfoundation.org/phage">Europe</a> but haven’t been approved in North America.</p>
<p>There are vaccines available for some bacteria, like the DPT vaccine against Diphtheria, <em>Bordetella pertussis</em> and <em>Clostridium tetani</em>. And there are plenty of simple solutions to <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/workplace-safety-infection-control">prevent bacteria from making us sick</a>, such as proper hand washing, disinfection of surfaces, use of clean water and cooking to appropriate temperatures to eliminate bacteria.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=471&fit=crop&dpr=1 600w, https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=471&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=471&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=592&fit=crop&dpr=1 754w, https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=592&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/112782/original/image-20160224-16425-vs02a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=592&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Leishmania mexicana parasites.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/wellcomeimages/19290103882/in/photolist-voAPPY-voAPLb-v7FC5D-v7FBZ8">Wellcome Images</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Parasites – benefiting at our expense</h2>
<p>The third group in our trio of pathogens – parasites – have inspired many <a href="http://thebrainbank.scienceblog.com/2015/10/20/aaahh-real-monsters-how-parasites-and-pathogens-colonised-fiction/">horror stories</a> and many of us find them kind of gross. </p>
<p>Parasites are a diverse group of organisms that live in or on a host (like us) and benefit at the host’s expense. Parasites can be microscopic single cellular organisms called protozoa, or bigger organisms like worms or ticks. Protozoan parasites are actually more closely related to the cells in our body than to bacteria.</p>
<p>Parasites are everywhere, and they can play <a href="https://theconversation.com/good-parasite-bad-parasite-nature-has-a-job-for-everyone-23279">a complex and important role in ecosystems</a>. </p>
<p>But parasites can also cause horrendous diseases, especially in the developing world. In many cases, infection with parasites goes hand in hand with bad sanitary conditions and poverty. Even though much progress has been made, <a href="http://www.unicef.org/health/files/health_africamalaria.pdf">malaria</a>, which kills one child every 30 seconds with 90 percent of the cases in Africa, is still the most deadly disease caused by parasites. But it is by far not the only one. </p>
<p>Other parasitic diseases common in many – mostly tropical – parts of the world are <a href="http://www.cdc.gov/parasites/leishmaniasis/">Leishmaniasis</a>, <a href="http://www.cdc.gov/parasites/onchocerciasis/index.html">River Blindness</a> and <a href="http://www.who.int/mediacentre/factsheets/fs102/en/">Elephantiasis</a>. </p>
<p>Many parasites are transmitted by mosquitoes and other insects, and with the effects of climate change intensifying, many <a href="https://theconversation.com/hard-evidence-will-climate-change-affect-the-spread-of-tropical-diseases-37566">parasitic diseases are likely to move farther north</a>. </p>
<p>Parasitic diseases are on the rise in developed countries, including <a href="http://www.cbsnews.com/news/parasites-causing-infections-in-the-us-cdc-says/">the U.S.</a> <a href="https://theconversation.com/explainer-what-is-chagas-disease-40047">Chagas disease</a>, for example, is caused by a single cellular parasite and <a href="http://dx.doi.org/10.1371/journal.pntd.0002300">cases are increasing in North America</a>, possibly aided by <a href="http://www.ncbi.nlm.nih.gov/pubmed/18686271">climate change</a>.</p>
<p>There are no vaccines available so far against any major parasitic diseases in humans, but there is plenty of research <a href="https://theconversation.com/new-malaria-vaccine-has-its-flaws-but-its-better-than-nothing-19020">on that front</a>. Luckily, there are many drugs available to combat parasites.</p>
<p>For instance, the 2015 Nobel Prize in Medicine was given to scientists who developed antiparasitic drugs (one drug, Ivermectin, <a href="https://theconversation.com/how-2015-nobel-prize-drug-might-rid-africa-of-ancient-scourges-48674">treats worms</a>; the other, Artemisinin, <a href="https://theconversation.com/nobel-prize-for-malaria-drug-is-crucial-to-control-africas-epidemic-48647">treats malaria</a>). </p>
<p>These two drugs have helped whole countries to manage scourges caused by <a href="http://www.nobelprize.org/nobel_prizes/medicine/laureates/2015/press.html">parasitic worms and malaria</a>.</p>
<p>The latest success was in September 2015, when <a href="http://blogs.biomedcentral.com/bugbitten/2015/09/11/good-news-mexico-river-blindness-eradication-confirmed/">Mexico eliminated River Blindness</a>, which is caused by <em>Onchocerca volvulus</em>, with the help of <a href="http://www.cartercenter.org/health/river_blindness/index.html">ivermectin donated by Merck</a>. </p>
<h2>Stay clean</h2>
<p>Getting a harmful virus, bacterial infection or parasite disease isn’t good news. Fortunately we have effective treatments for some of them, and vaccines that can prevent us from getting sick as well, even if some of these bugs can evade the best medicines we have.</p>
<p>And keep in mind that even if these bugs can make us very, very sick, you still need to be exposed to them to become infected. While bigger strategies, like sanitation and infection control can keep us and others safe, so can simple strategies, like washing our hands, staying home when we are sick and covering our mouths when we cough or sneeze.</p><img src="https://counter.theconversation.com/content/49695/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 organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>What is the difference between these pathogens, and how dangerous are they?Arinjay Banerjee, PhD Student in Veterinary Microbiology, University of SaskatchewanJason Byron Perez, MSc Student, University of SaskatchewanSimona John von Freyend, Research Fellow, Malaria biochemistry, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.