Rachel Fieldhouse IN June last year , Chief Medical

Officer Professor Paul Kelly declared the end of a national emergency response for an unpredictable and deadly viral disease .

No , this was not COVID-19 but the Japanese encephalitis virus ( JEV ).

Beginning in March 2022 , across the temperate inland areas of NSW , Victoria and SA , 45 confirmed JEV cases were recorded , including seven

“ We can guess that it has something to do with flooding events and a change in the dispersal patterns of wild bird hosts that then infected pigs that maybe infected humans .

“ And why did it disappear ? Did all the virus hosts fly away , or was the virus so widespread that everything became immune ?”

The spread of JEV into southern Australia also remains a mystery .

According to the national Consultative Committee on Emergency Animal Diseases , its “ rapidity and extent of spread ” were not expected .

“ The evidence currently available suggests that the virus is widespread … and present in feral pigs and vectors , which may provide an environmental reservoir for the virus , meaning eradication is therefore unlikely ,” the committee wrote .

However , without the co-ordination of the national emergency response , Professor Devine warned that health officials may only have a “ fragmented ” picture of the virus ’ future spread when it re-emerged .

“ At the beginning of the outbreak , and it ’ s still pretty much the case now , it was really hard to know where the human infections occurred across Australia .

“[ It is of note ] that , in contrast , the veterinary community published all their findings on infected pig herds .

“ We need to know what are the transmission pathways , where are the populations at risk and where do we need to target the existing vaccines .”

He added : “ If we don ’ t do that , then I ’ m not sure that public health authorities are doing their duty .”

Associate Professor Greg Devine .

deaths .

It marked the first detection

of locally acquired cases on the

mainland since 1998 and triggered

increased surveillance

and removal of potential mosquito

breeding sites .

Additionally , more than

125,000 vaccine doses were

administered to patients at

high risk of infection , including

workers at piggeries .

While the perceived threat

of JEV has died down , there

are some who believe that

Professor Kelly ’ s words were

premature .

“ It is entirely possible that

something like JEV or Murray

Valley encephalitis may

well emerge in the near future ,

especially with the anticipa-

‘ Did everything become immune ?’

tion of another La Niña season

with increased rainfall patterns

,” says Associate Professor

Greg Devine , who leads the

mosquito control laboratory

at Brisbane ’ s QIMR Berghofer

Medical Research Institute .

One of the aims of the

national emergency response

was to improve understanding

of how JEV spreads .

The outbreak was genetically

traced back to a sentinel

case detected a year earlier on

the Tiwi Islands , about 80km

north of Darwin .

The 45-year-old patient

had presented with a twoday

history of acute confusion

and fever , according to a

case report in The New England

Journal of Medicine . They were

admitted to hospital with progressive

neurological deterioration

but died 15 days later .

The treating doctors had

obtained a complete JEV

genome sequence from thalamus

tissue during post-

mortem histological analysis ,

which they said was “ closely

related ” to strains later identified

in local pig , human and

mosquito samples .

But Professor Devine — a

medical entomologist who

co-authored a paper that compared

this genotype isolate

with historical JEV isolates —

said it was still unclear how the

recent outbreak had started or

why it had ended .