Ross River Virus: Many Vectors and Unusual Hosts Make for an Unpredictable Pathogen.

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While most mosquito-borne viruses are associated with a narrow range of vector and reservoir host species, some pathogens have much larger vector and host assemblages. One such group is the Alphaviruses (including chikungunya virus [CHIKV]), with Ross River virus (RRV), endemic to Australia, providing a fascinating example of the complicated relationship between vector and reservoir host species across different environments (Fig 1). RRV is responsible for the most commonly reported mosquito-borne disease in Australia, and as both a reservoir host and vector generalist, the virus has complex spatial and temporal activity that makes outbreak prediction, vector and pathogen surveillance, and public health risk mitigation strategies difficult. Here, we review the unique ecology of RRV and the challenges it presents for local health authorities. Fig 1 There are complex relationships between the vectors and the zoonotic reservoirs of Ross River virus across coastal, inland, and metropolitan regions of Australia. Ross River Virus Disease Ross River virus disease (also commonly known as Ross River Fever) is not fatal. However, the associated arthralgia can be seriously debilitating. While there are a wide range of disease symptoms, they typically include arthritic joint pain, usually of the peripheral joints, which affects 83%–98% of patients; fatigue and rash, both of which affect over 50% of patients; and fever, which affects 20%–60% of patients [1]. The severity of symptoms varies, as does their duration, which can range from a few weeks to several months [2]; several studies indicate that chronic joint pain affects over 50% of RRV disease patients, which can persist for years after diagnosis [1]. The public health impacts of RRV disease are significant: it is estimated to cost Australia at least US$4.1–US$4.7 million per year [3]. The incidence of RRV disease varies regionally [2]. Roughly 5,000 cases of RRV disease are officially notified each year [4]. There are generally more cases recorded in northern Australia, but the virus still poses a substantial threat in the temperate southern regions of the country. RRV disease case numbers are generally thought to be an underestimate [5]. Accurately quantifying the scope of RRV disease is difficult, as the variability in symptom severity and the requirement of a blood test to confirm infection may cause many milder cases to go undiagnosed. As a consequence, official statistics may only represent the most severe cases. There are no specific treatments available for the disease; patients are usually given supportive care and prescribed general analgesics and anti-inflammatory agents to treat symptoms [1]. While a vaccine is in development [6], current prevention strategies rely primarily on mosquito avoidance and control.