Australia records disturbing uptick in Murray River encephalitis

A deadly mosquito-borne disease that kills about one in five of those who catch it is rising across Australia.

State health agencies from Queensland to Western Australia have recorded a troubling uptick in Murray River encephalitis cases, a rare but dangerous illness that can kill or lead to permanent neurological damage such as paralysis and brain damage.

NSW Health has recorded six cases of Murray River this year compared with zero cases in 2022, a single case in 2021 and zero cases in 2020 and 2019.

Queensland Health has recorded two cases this year compared with none in the previous four years to 2019.

South Australia has also recorded a case of the disease, characterised by fever, headache, nausea and vomiting, its first in the past five years.

In Western Australia, two people have died from the disease this year, including a child who died after being bitten in the West Kimberley region in March.

In February, Victoria recorded its first case and death from Murray River encephalitis since 1974 after a woman in her 60s died from a bite.

There is no treatment for Murray River encephalitis and SA Health recommends the best defence is to avoid being bitten in the first place.

“People should use mosquito repellents containing either DEET, picaridin or oil of lemon eucalyptus that have been approved by the Australian Pesticides and Veterinary Medicines Authority,” the agency states.

Flood events, such as the River Murray flood in SA between November 2022 and February 2023 or the Kimberley flood in WA over the New Year period can lead to an increase in mosquito breeding.

And while an expected El Nino-driven surge in hot, dry weather could reduce mosquito numbers in inland Australia, University of South Australia professor Craig Williams said the major population centres would likely remain vulnerable.

“The cities are by the sea, so you’ll have coastal mosquitoes, which will continue to breed and they are not always driven by rainfall, but their breeding sites can be from tidal action,” he said.

“There’s also urban mosquitoes that are in the built-up areas of the city that will continue to do well.”

Cases of other mosquito-borne diseases such as Ross River and dengue fever fluctuate from state to state but tend to show stable or declining numbers.