More than just itchy and inconvenient, mosquitoes — and their bites — are a cause for serious concern in southern Australia.
Rural Doctors Association of Australia president Megan Belot lives in central Victoria near the Murray River, and near where Japanese encephalitis virus was detected at several piggeries earlier this year.
"Every season when we see the mosquitoes come back there's always the issue around Ross River," Dr Belot said.
"But the question at the forefront of everyone's minds this year is will Japanese encephalitis virus return?"
Dr Belot said she "would have loved to have been able to vaccinate [her] family" when the virus was first detected.
Most people who contract the virus will have very mild symptoms — or none at all — but an unlucky few, fewer than 1 per cent, will experience a severe infection.
Victoria deputy chief health officer Deborah Friedman said Victoria, New South Wales, and South Australia had "never ever" had locally acquired cases of the virus before.
Five Australians have died, and 40 human cases of the virus and suspected cases have been reported in people across the country.
Department of Medical Entomology principal hospital scientist Cameron Webb said it was unclear what it would mean in terms of further cases during summer.
"There's not a lot to go on in terms of predicting how well it'll persist," Dr Webb said.
A NSW Health spokesperson said the department was "uncertain" whether or not it would return again this summer, "since the ability of the virus to survive in dormant mosquito eggs depends on a complex interplay of weather and environmental factors".
A Department of Health and Aged Care spokesperson said response planning was under way for the warmer months.
The spokesperson said $69 million had been spent on the response to the outbreak.
"A future vaccination strategy is in development in collaboration with the National Centre for Immunisation Research and Surveillance and the Communicable Disease Network of Australia," the spokesperson said.
The perfect combination
Many of the cases have been linked to the New South Wales and Victorian border where Dr Friedman said the Murray River had provided the "perfect combination of the appropriate animal vectors and the appropriate climate and water", as wading water birds and pigs could carry the virus.
There was hope that weather patterns in the coming months would better protect Victoria but along the border, Dr Friedman said "the risk may certainly remain".
Where do mosquitoes go when it's cold?
Dr Webb said the activity of mosquitoes — like most insects — was driven by temperature.
Some "low-level mosquito activity" continued over these colder months but most mosquitoes were in an "almost" hibernation, "hiding away in cracks and crevices".
Dr Webb said mosquitoes could also survive in unhatched eggs laid in mudflats, wetlands and bushland areas, and would start hatching with the arrival of warmer weather, longer days, and water.
"There's always a chance that [the virus has] remained circulating in mosquitoes and wildlife," Dr Webb said.
Dr Webb said the arrival of Japanese encephalitis virus in Australia was likely to be in part due to "two summers dominated by La Niña weather patterns", while drought conditions would mean a decline in mosquito and some waterbird populations.
"Increasingly frequent extreme weather events, warmer autumns, warmer springs could mean the potential extension of the mosquito season," Dr Webb said.
Winter respite
Victorian authorities have turned their attention toward promoting the vaccine.
Eligibility for the free vaccine was given to priority groups, those who worked or lived at a piggery or worked directly with mosquitoes, or laboratory workers who risked being exposed to the virus.
Several thousand people have been vaccinated in Victoria, and authorities will target eight highest-risk local government areas to increase vaccination uptake among those already eligible.
Dr Friedman said the cost of a doctor's appointment was a likely barrier for some, but when a public health emergency order was issued it meant that nurse immunisers, not just doctors, would be able to administer the vaccine.
But the supply of vaccines would be limited because it was produced overseas.
"What we need to do in each state individually, is to look at our different local government areas and determine which people are the highest risk," she said.
NSW and Victorian authorities are also working to determine the prevalence of the virus in the wider community by testing blood samples.
The advice
The health advice is simple. Avoid being bitten by mosquitoes.
Wearing loose-fitting clothing, using mosquito repellent, and using coils, screens and vaporisers were recommended.
Dr Belot said it was not just the new risk of the virus to be concerned about.
She said Ross River fever could be an ongoing and debilitating condition.
"I think we just need to be proactive and be ready," Dr Belot said.
