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Explainer: what is Ross River virus?

Ross River virus infection is the most commonly reported mosquito-borne disease in Australia, with more than 4,000 cases of illness are reported every year. Activity has been recorded from every state…

The saltmarsh mosquito, Aedes vigilax, transmits Ross River virus in many coastal regions of Australia. Mr Stephen Doggett (Medical Entomology, Pathology West - ICPMR Westmead)

Ross River virus infection is the most commonly reported mosquito-borne disease in Australia, with more than 4,000 cases of illness are reported every year.

Activity has been recorded from every state and territory in the country. And while Ross River virus generally considered a disease of rural regions, it is increasingly active at our urban fringes.

Symptoms

Ross River virus is not fatal but it can be debilitating. The symptoms typically include “flu-like symptoms” such as fever, chills, headache, muscle and joint pain and a general feeling of fatigue.

The symptoms develop a week or so after being bitten by an infected mosquito. But while they typically last less than two weeks, there are cases where fatigue, muscle and joint pain persist for many months.

Ross River virus is a notifiable disease, so infection can only be confirmed through a blood test. For this reason – and because the severity and duration of symptoms can be highly variable – it is strongly suspected that many cases go unreported and that the official statistics are a dramatic underestimate of the total number of infections each year.

There are no specific treatments or vaccines, so preventing mosquito bites is critical in avoiding disease.

It’s difficult to predict outbreaks and governments don’t have the capacity to undertake broad-scale mosquito control in all regions, so health authorities generally focus their efforts on raising awareness and issuing warnings, based on information from local surveillance programs.

Transmission

There are more than 40 mosquito species that may play a role in transmitting the virus. This is a problem because the mosquitoes transmitting the virus during outbreaks may vary from region to region, making it difficult to track.

It is also a problem because the environmental drivers of mosquito abundance will change from region to region. This means that in some locations, the risks of an outbreak may be triggered by rainfall while in others, it is the tidal flooding of coastal wetlands.

While it is not surprising that outbreaks generally occur when mosquito populations are high, abundant mosquito populations and wetlands don’t guarantee an outbreak will occur.

Mosquitoes generally don’t hatch out of the wetlands infected with Ross River virus, they must bite an infected animal first. The most important reservoirs for Ross River virus are macropods (kangaroos and wallabies).

Kangaroos and wallabies are critical in determining the risks of Ross River virus. Dr Cameron Webb (University of Sydney and Pathology West)

There have been Ross River virus cases from most of our major metropolitan centres. In many urban fringe areas, newly constructed wetlands are increasing the abundance of local mosquito populations, while the control of foxes and feral cats has led to an increase in populations of wallabies.

Wallabies using the bushland corridors along our rivers and estuaries therefore may be increasing the risks of Ross River virus. This potential has been illustrated by the recent public health warnings issued due to the detection of Ross River virus in mosquitoes collected along the Georges River in southern Sydney where wallabies are common within Georges River National Park.

Prevention

It’s important to protect yourself from mosquito bites with protective clothing or topical insect repellents when you’re around wetland and bushland areas, particularly at dawn and dusk when mosquitoes are most active.

Remember, even though mosquito populations are falling, autumn is actually the peak period of virus activity. You may not be swamped by mozzies but you should still take precautions to avoid bites.

Join the conversation

16 Comments sorted by

  1. John Campbell

    farmer

    I presume Ross River virus is named after the Ross river in Townsville?

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    1. Cameron Webb

      Clinical Lecturer and Principal Hospital Scientist at University of Sydney

      In reply to John Campbell

      Yes, you're right John. As is the case for other mosquito-borne viruses, the name comes from the location where it is first isolated and described.

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    2. Eric Thacker

      Viticultural Contractor

      In reply to John Campbell

      It is. I can recall researchers putting requests on noticeboards at JCUNQ's Townsville campus asking for students who were not from NQ to volunteer for blood tests to track exposure to it.

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  2. Colin Samundsett

    retired BSurv

    I note that you dote on the gormless host of the disease as being the macropod. However, the NSW Arbovirus Surveillance & Mosquito Monitoring Program sees fit to publish only Mosquito/Chicken Results. How so, that the marsupial (so often regarded as something of "that maundering" ilk) is the one wot cops the blame?

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    1. Cameron Webb

      Clinical Lecturer and Principal Hospital Scientist at University of Sydney

      In reply to Colin Samundsett

      In relation to public health importance, macropods are the key reservoir hosts of the virus. The NSW Health surveillance program tests mosquitoes for the presence of the virus. Sentinel flocks of chickens are also part of the NSW Health program across inland regions but these do not target Ross River virus, instead, they target those mosquito-borne pathogens closely associated with birds including Murray Valley encephalitis virus and Kunjin virus. There is no systematic program in place anywhere in Australia that monitors macropods for activity of Ross River virus.

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  3. Paul Prociv

    ex medical academic; botanical engineer at University of Queensland

    Thanks for bringing this infection to attention, but I’m disappointed that so few statistics are presented, particularly relating to its public health significance, i.e. clinical vs. subclinical infections. I suspect the huge majority of people who become infected with RRV remain asymptomatic, or have such mild and/or vague symptoms that they don’t bother seeking medical attention.
    While it might seem pedantic, I must raise an objection to some poor expressions in the article, which reflect the…

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    1. Cameron Webb

      Clinical Lecturer and Principal Hospital Scientist at University of Sydney

      In reply to Paul Prociv

      Thanks for the feedback. I agree with the comments, perhaps "Ross River virus disease" should have been used throughout but I suspect readers understand that it is the illness caused by this virus being discussed. You're also right about asymptomatic infection as noted in the piece "it is strongly suspected that many cases go unreported and that the official statistics are a dramatic underestimate of the total number of infections each year". It isn't just cases with mild symptoms that don't present to a GP that go unreported, unless there is a blood test to confirm infection, cases won't be included in statistics.

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    2. Fron Jackson-Webb

      Section Editor at The Conversation

      In reply to Cameron Webb

      Hi Paul, Cameron's initial draft actually referred to Ross River virus disease/infection, but I shortened it to Ross River virus in the editing process. Thanks for the clarification.

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  4. Katrina Alilovic

    Psychologist

    Thanks for this article. I'm very interested as I live nearby a river and have been alarmed by the prevalence of mosqitoes in the area. I've returned to Australia after over 10 years away in the UK and hadn't expected the mozzies, nor how they adversely impact on the 'outdoors lifestyle', and the potential for infection from bites. I can't find anything on my local council website about a planned response to managing the situation. You state in your article that governments don't have the capacity to undertake broad scale control measures. I'm interested in what could be done if they did have the capacity or if it was decided to be a health priority. Can you say some more about what might be possible in addition to personal prevention plans. many thanks

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    1. Cameron Webb

      Clinical Lecturer and Principal Hospital Scientist at University of Sydney

      In reply to Katrina Alilovic

      Hi Katrina, it is a complex problem to solve! Controlling mosquito populations is one strategy and local councils are generally responsible for this. Studies have indicated that mosquito control in all local mosquito habitats is required to significantly reduce the risks of Ross River virus. As so many different mosquito species, associated with a wide range of habitats (from estuarine saltmarshes to freshwater wetlands to backyard rainwater tanks), may be involved in transmission, it is difficult…

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    2. Beams Mlb

      retired

      In reply to Cameron Webb

      When one balances the effects of Ross River Virus with the health of the community, it is difficult to accept that the costs are prohibitive. A citizen who is also a landlord cannot cry poor if the health of the tenant is jeopardised by the lack of standards in the building he/she rents, so why is the Council not required to safeguard the community's health. I cannot see how a large area can be rid of mosquito infestations unless a central body is responsible to act totally over the area.
      I speak of Harwood in the North Coast NSW that is so badly infested that one time I came out of my car and was hit by a seemingly 'solid' curtain of mozzies. The council's report confirmed the presence of Virus carrying mosquitos.
      It reminded me of a horror movie.
      Shouldn't the health of the community be a priority expense?

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    3. Paul Prociv

      ex medical academic; botanical engineer at University of Queensland

      In reply to Beams Mlb

      Your comment sounds reasonable at first glance, and does reflect what many people think, but it also betrays a lack of knowledge of the sheer complexity of mosquito diversity and biology. We have numerous mosquito species, whose biological needs and behaviour vary amazingly. Some have very specific feeding times, others are extremely pernickety about where to lay their eggs, and so on. And they all share their habitats with diverse other organisms that are important components of complex eco-systems…

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  5. Dianna Rejman

    logged in via Facebook

    I live near a wetlands north of Adelaide in SA. At the time people first started to get infected in the area, I thought that the aerial spraying of insecticides seemed to me to be more dangerous than the disease. I advocated and suggested that ridding properties in the area of stagnant water pools in old tyres, pots and ground water (puddles)etc. and introducing large numbers of suitable fish to the wetlands might be more appropriate. Unfortunatley the poison spraying voters won out! It worked in the short term with the mozzie plague but killed all the frogs and many other environmentally important creatures.

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  6. Dianna Rejman

    logged in via Facebook

    Can anyone tell me if having had RRV gives one immunity to re-infection? Also Is it possible that the range of arthritic symptoms, the fatigue and headaches reported by so many could be constant companions, as suggested by other sufferers, many years after infection? Or is it that the people who are bitten and continue to suffer have arthritic genes and would have suffered these symptoms anyway, perhaps at later onset? I can't seem to find any clinical studies on this and given that it has been around for so long, this surprises me.
    I have noticed that my blood tests show IgG Positive and IgM Negative, can anyone explain this to me?

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  7. Dianna Rejman

    logged in via Facebook

    I have heard that spraying Listerine, (a well known mouthwash brand), around an area gets rid of, ? repels or kills Mozzies from that area. Has anyone done any research on this?

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