Victoria Health officials issued a health warning Wednesday concerning mosquitoes and the risk of Ross River virus and other vector borne infections.

Residents and visitors to Victoria are being warned to protect themselves against mosquito-borne diseases such as Ross River virus, Barmah Forest virus and Murray Valley encephalitis.


A number of residents of outer metropolitan Melbourne have been notified to the Department of Health and Human Services with Ross River virus infection, and have not travelled to areas where mosquitoes that carry the virus are usually found.

Sky News reports that more than 600 Victorians have tested positive for Ross River virus in the past six weeks. ‘Recent rain and relatively warm weather has created conditions ideal for mosquito breeding and we have seen a significant increase in mosquito numbers as a result,’ Victorian Chief Health Officer Charles Guest said on Wednesday.

There have been recent findings of Ross River virus in mosquitoes trapped within the Frankston municipality, and a finding of Kunjin/West Nile virus in a sentinel chicken flock in Shepparton. These findings are a reminder of the importance of protecting against mosquito bites, and of the need to ask patients about exposures when presenting with a compatible illness.

Anyone is potentially at risk of being bitten by mosquitoes and while most bites will only cause minor swelling and irritation, an infected mosquito can transmit potentially serious diseases. All parts of Victoria where there are mosquitoes may carry a risk for Ross River virus infection, although the risk is greatest in regional Victoria. Infection appears to be rare in outer metropolitan areas.

Ross River virus and Barmah Forest virus disease cause a similar illness. Both can cause joint swelling and pain, fatigue and muscle aches which can persist for many months. A rash and fever may also develop. It takes three to nine days for symptoms of Ross River virus disease to occur after exposure, and occasionally up to 21 days. Barmah Forest virus disease symptoms occur between seven to ten days after a bite from an infected mosquito. Symptoms for both conditions usually resolve within 4-6 months. Affected individuals also develop immunity to subsequent infection.

Murray Valley encephalitis symptoms commence between seven to 28 days after exposure and include fever, headache, nausea and vomiting. This can lead to meningitis or encephalitis, which can lead to drowsiness, confusion, fitting, weariness or unsteadiness. In severe cases, delirium and coma can follow, resulting in brain damage or death. Kunjin/West Nile virus can cause symptoms similar to Ross River virus infection, and rarely leads to encephalitis. The incubation period is unknown, but is likely to be from 2-14 days.

The best protection from mosquito-borne diseases is to avoid mosquito bites – use mosquito repellent containing picaridin or DEET, wear long and loose fitting clothing when outside, and ensure accommodation is mosquito proof.