“Vaccination is an important part of the public health response but,currently,global supply of[the] vaccine is very limited,so we’re urging people to protect themselves by avoiding mosquito bites altogether,particularly as we head into warmer months,” Chant said.

Scott Ritchie,a professor at the Australian Institute of Tropical Health and Medicine,said the parameters of the study and the absence of cases in mainland Australia for decades meant that the extra cases detected through the serology survey were “undoubtedly” part of the outbreak,rather than infections picked up at an earlier time.

With another wet summer forecast for the state,Ritchie said it was likely Japanese encephalitis would be detected again this summer. However,transmission patterns may be smaller even if the number of official cases rise.

“Diseases that are new come into a naive population,so you have this big explosion in cases,” he explained. “But then in the following years you’ve got some degree of herd immunity,including in animals.”

“I can’t imagine transmission will be as great as it was last year,but you need to remember that we will be looking for it. So we could have less transmission but pick up more cases because people are testing and aware of the symptoms.”

Dr Ali Zaid,a viral immunologist at the Menzies Health Institute in Queensland,said it was “reasonable to assume” the previous infections were from this year,although the asymptomatic nature of most Japanese encephalitis cases meant previous outbreaks in mainland Australia may have been missed.

He said mosquito-borne viruses would be an ongoing problem.

“Even before the second La Nina event was announced,around the time the Northern Rivers areas was really underwater,it was already apparent there would be enough waterlogging for the mosquitoes to breed and continue their cycle,” he warned.

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