Are you Familiar with the Risks of Ross River Virus Infection?
Published: 09 December 2020
With recent spikes in the number of reported cases of Ross River virus infection in Australia (Burnie 2020; Ward 2020), it is an important time to familiarise yourself with Australia's most common mosquito-borne infection.
Ross River virus (RRV) infection, also known as Ross River fever or epidemic polyarthritis, is endemic in Australia, Papua New Guinea, parts of Indonesia and several islands in the South Pacific (NTG 2020). It is the most common arbovirus infection in Australia (NSW DoH 2016).
The largest outbreak in Australia occurred in 2015, where there were over 9000 cases notified - with more than 6000 of them from Queensland. Such epidemics relate to favourable mosquito breeding conditions such as heavy rainfall, floods, high tides and high temperature (Murphy et al. 2020).
On average, there are about 4000 cases of RRV in Australia every year, with about half of these occurring in Queensland. The virus is also common in the Northern Territory and the Kimberleys in Western Australia, where they tend to peak in the summer and autumn wet season, especially between January and April (Healthdirect 2020; Murphy et al. 2020). In the south-west of Western Australia, the season peaks in spring and summer (WA DoH 2020).
Of the more than 40 species of mosquito (WHA 2015) that have been found to be capable of carrying the virus, the most important are:
Culex annulirostris (common banded mosquito; breeds in permanent bodies of fresh water);
Ochlerotatus vigilax (salt marsh mosquito of northern Australia; breeds in salty pools in mangroves and salt marshes after flooding by spring tides and heavy rains; aggressive biter during day and night);
Ochlerotatus camptorhynchus (southern Australian salt marsh mosquito);
Aedes notoscriptus (backyard mosquito; breeds in containers close to homes and other human activity) and
Ochlerotatus normanensis (flood water mosquito; breeds in temporary ground pools in drier areas of northern Australia).
(NTG 2020; WHA 2015)
Causes and Transmission of RRV
Mosquitoes are believed to pick up the virus from as kangaroos, wallabies, possums, wombats, wild rodents, birds, flying foxes, dogs, horses, cattle and possibly humans (Murphy et al. 2020; Skinner, Webb & Flies 2019). The virus enters the bloodstream through saliva from an infected mosquito, reproduces in red cells, then in muscles, joints and skin (ABC Health 2015).
There has been one reported case of transfusion-transmitted infection (Hoad et al. 2015).
Symptoms of RRV
Many of those infected do not develop any symptoms. This is especially true of children, who generally only experience mild symptoms that last for a shorter length of time, if any (NTG 2020).
Most cases are in adults aged 30 to 64 years (Murphy et al. 2020). The incubation period is usually 7 to 14 days, but symptoms can develop anywhere between 3 and 21 days after being bitten (NTG 2020).
Severe pain in multiple joints (usually the wrists, knees, ankles, fingers, elbows, shoulders and jaw) and stiffness (that may be particularly noticeable in the morning) are common symptoms. The joints may also swell (Healthy WA 2013; NSW DoH 2016).
Other symptoms may include:
Fatigue and lethargy;
Flu-like symptoms (fever, chills, headache and pain in muscles, ligaments and tendons surrounding joints);
Raised, red rash on limbs, trunk, face, hands and feet that generally disappears after 7 to 10 days;
Swollen lymph nodes;
General feeling of being unwell;
Sore eyes and throat;
Tingling on soles of feet and palms;
(NSW DoH 2016; NTG 2020)
Symptoms usually resolve within six weeks, but in some cases, they may last for months or even up to one or two years. In about 10% of cases, people will experience ongoing depression and fatigue (SA Health 2020). There have been a few instances of reinfection, but in most cases, getting RRV once should guarantee lifelong immunity (NTG 2020).
Diagnosis is by blood tests for antibodies. A rise in IgG antibody over two to four weeks is the most useful. In many viral diseases, testing for IgM antibody can show a recent infection, but in Ross River virus infection, this antibody can persist for anything up to two years, and false positives are not uncommon (Lab Tests Online 2018).
It may be necessary to eliminate other causes of similar symptoms, such as dengue, Barmah Forest virus, infectious mononucleosis, rubella, Q fever, rheumatoid arthritis and systemic lupus erythematosus (Barber, Denholm & Spelman 2009).
Treatment of RRV
Treatment is non-specific. Anti-inflammatories such as ibuprofen seem to provide the most effective relief. Aspirin (not for children under the age of 12) or paracetamol may be useful. A combination of plenty of rest and gentle exercise is important to keep joints moving and to prevent over-tiredness (SA Health 2020; Healthy WA 2013). A trial is currently being undertaken of treatment with Pentosan Polysulphate Sodium (Lyell 2017).
Prevention of RRV
Protect yourself from mosquito bites by:
Avoiding periods of heavy infestation (early evenings and dawn in warmer months);
Using insect repellent;
Wearing protective clothing in light colours;
Screening living and sleeping areas; and
Removing potential mosquito breeding areas (uncovered, still water containers).