Mosquito numbers and the risk of mosquito-borne diseases are likely to increase this spring and summer in river communities as La Nia brings wet conditions to large parts of the country.
As the weather warms, some areas of eastern Australia are still dealing with ongoing floods, while others in southern parts of the country start to see the impacts of flood waters from upstream.
The CSIRO says this creates the perfect breeding conditions for mosquitoes.
"Anywhere you've got shallow [pooling] water, it's an ideal habitat for mosquitoes such as Culex annulirostris," said CSIRO principal research scientist Paul De Barro.
"Even though you might not have flooding directly in your area, it can fly tens of kilometres, so it can move inland quite some distance as it's assisted by wind."
A common species of mosquito that thrives in wetter conditions, the Culex annulirostris is also a carrier of arboviruses, including the Japanese encephalitis virus (JEV).
JEV can cause a potentially fatal inflammation of the brain in less than 1 per cent of people.
"It could well be a problem again this year because the conditions are very similar to last summer when the virus was detected in Australia," Dr De Barro said.
He says, unfortunately, there is not much that can be done to reduce mosquito populations, but it is critical people take adequate precautions.
Concerns cross borders
NSW Health Pathology's Cameron Webb is equally concerned about JEV.
"It can survive in the mosquito eggs on the edge of wetlands and floodplains or even in those mosquitoes that [live] in the winter months in very low numbers," he said.
For Robbie Alexander, who has lived in north-east Victoria all of his life, a mosquito increase is a concern.
While a JEV vaccination is available to eligible people in his local area, he's still worried about the prospect of being bitten.
"It's a concern. Catching COVID is a concern, catching the flu is a concern. JEV is just another thing to be worried about," he said.
Nationwide monitoring off and flying
In South Australia, there are five human cases of JEV with a statewide trapping program that has been increased from monthly to fortnightly and expanded to council areas outside of those in close proximity to the Murray River.
All trapped mosquitoes are sent to the Victorian Agriculture Department to be screened for arboviruses including Ross River Virus and Barmah Forest.
Meanwhile, upstream and across the border in neighbouring Mildura, weekly mosquito trapping is underway, with decisions about spraying to be made on a regular basis.
"What we can all do is address any breeding sites that might be around the home and remove any stagnant water where we can," said Mildura Rural City Council environmental health coordinator Alana Nolen.
