Ross River virus activity ramps up

4 minute read

Health experts are warning we could be in for a spike in cases of the mosquito-borne virus over the coming months.

Australian health authorities are warning of a looming spike in Ross River virus infections following a sharp rise in the detection of mosquitoes carrying the debilitating virus.

Latest data from the National Notifiable Disease Surveillance System showed there has been 206 notifications of Ross River virus across the country between January 1 and February 15.

The bulk of cases have been in Queensland (135), followed by Western Australia (29), NSW (21), the Northern Territory (10), Victoria (eight) and Tasmania (one). The ACT is the only jurisdiction in the country to have zero cases so far this year.

Ross River virus is not the only mosquito-borne disease to be circulating around Australia this summer.

For 2024 to date The National Notifiable Disease Surveillance System has recorded 125 cases of Dengue virus, 54 cases of malaria, 28 cases of Barmah Forest virus, seven cases of Chikungunya virus and one case of Flavivirus (unspecified).

While there have been no reported cases of the potentially deadly Japanese encephalitis and Murray Valley encephalitis in Australia this year, virus activity has been identified in some parts of Australia.

Queensland chief health officer Dr John Gerrard said there had been a very high number of Ross River virus detections in mosquitoes across nine different local government areas in recent weeks, stretching from Mackay down to south-east Queensland.

“Queensland Health, together with local government partners, routinely collects mosquito samples and tests them for Ross River virus infection. This season, more than 700 mosquito trap collections have been tested for Ross River virus,” he said.

“We have been notified of 31 positive mosquito traps across the state so far, which is more than the total we saw over the 2019-20 summer months when there was a significant Ross River virus outbreak. In 2020, 3381 cases of Ross River virus were recorded.

“It’s concerning we are seeing such a high number of Ross River virus detections in mosquito populations through our surveillance program this early in the typical season, especially over such a widespread area. This is an indicator of elevated virus activity.”

Symptoms of Ross River virus may include fever, swollen and painful joints and rash. Treatment is supportive and involves managing symptoms. While most people recover in a few weeks, some people experience joint pain and fatigue for months after the infection and may require referral for specialist treatment.

Mosquitoes are vectors of the virus, becoming infected after biting an infected animal then transferring the virus to humans through biting. The virus cannot spread from person to person.

University of Sydney Associate Professor Cameron Webb, principal hospital scientist in the Medical Entomology department at NSW Health Pathology, agreed all signs pointed to a spike in Ross River virus cases in Australia this year.

“One of the reasons why we’re all mindful about Ross River virus is that we generally see major outbreaks every two or three years,” he told The Medical Republic.

“On the east coast of Australia, the last time there was a really big outbreak was in 2020, and we’re now a few seasons on without any major activity. So that’s one of the reasons why we’re very mindful about that.”

Professor Webb said that typically, the period of greatest risk for Ross River virus and other mosquito-borne diseases was between February and March.

“It’s those next couple of months which have the highest risk,” he said.

“The first hint of it will, of course, be the detection of viruses in mosquito samples. But it can sometimes be anywhere up to a month delay between somebody being bitten by an infected mosquito, and then the notification of disease appearing in the official statistics.”

Professor Webb told TMR GPs had an important role to play in helping manage mosquito-borne diseases, not only by identifying and treating cases when they arise but also through prevention.

“If GPs are seeing people who’ve come back from summer holidays, up or down the coast back to metropolitan areas, it’s important to be mindful [of] Ross River virus and Barmah Forest virus,” he said.

In addition, he advised to stay up to date about outbreaks of these mosquito-borne diseases especially Japanese encephalitis.

“When you’re dealing with patients that are living and working in western New South Wales, they should be mindful about the availability of a Japanese encephalitis vaccine. That’s the only mosquito borne disease in Australia that where there’s a local risk there is a vaccine available,” he said.

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