South Australia has recorded four cases of Japanese encephalitis virus (JEV), with health authorities saying a person who died may also have had the mosquito-borne virus.
The four cases — two of whom remain in hospital, with the other two discharged — are the first detected in humans in SA amid the current national outbreak, the state's Department for Health said.
The department recently began an investigation into 10 people who had been infected and then hospitalised with acute encephalitis in the past month.
That led to the identification of the four cases with JEV.
One of the acute cases has died, but the health department's executive director of health protection Dr Chris Lease said it was not clear if they had JEV.
"It's a little bit late to tell, unfortunately," Dr Lease said.
"We're still investigating the other cases of encephalitis to confirm as far as we possibly can what the cause of their encephalitis might be."
Three of the four confirmed JEV cases were acquired locally, and seven of the 10 people are still in hospital.
Earlier this week, Australia's Chief Veterinary Officer said animals at 21 piggeries in four states including SA had been infected.
"We do have an effective vaccine, which is very reassuring," Dr Lease today said.
"We are looking to roll out the vaccine more extensively, really targeting those people most at risk — one group in particular are the folk who are actually going out doing our monitoring."
He warned that while most people who contracted it would be asymptomatic, the virus could prove fatal and cause long-term neurological damage.
He urged the public to avoid exposure to mosquitoes and take extra precautions ahead of traditional travel periods.
"People planning activities around the River Murray are warned to be especially vigilant, particularly between dusk and dawn when mosquitoes are most active."
Cases have also been detected in Victoria, New South Wales and Queensland.
"We really are, as a country, facing something we haven't seen before," Dr Lease said.
"There is a number of ecological theories why this might have occurred. The increased rainfall is one.
"There are also theories about mosquitoes being blown further south by things like cyclones as well."
