Killer mozzie virus was actually in Australia a year earlier than first thought

A woman from the Tiwi Islands, offshore from Darwin, was the first victim of the outbreak in early 2021.

Australia's leading experts in the area say the deadly virus may now be endemic, meaning it is here to stay.

Those scientists also say plans for a "possible" national rollout of vaccines for the Australian population will depend on how the virus survives the winter and "reemerges" this summer.

There are already plans in some states to extend vaccination programs beyond piggery workers to include older people working outdoors like farmers in mosquito hotspots.

The ongoing surveillance of commercial piggeries plus the sampling of mosquitoes and feral pigs will determine the next steps.

Now we know the outbreak was actually triggered a year earlier, with possible implications for a multitude of other diseases and viruses threatening the nation, like foot and mouth disease.

The nation was only alerted to the arrival of JEV in late February this year when the virus had already taken hold in piggeries in Victoria, Queensland and New South Wales.

Cases of JEV were detected in South Australia on March 4.

Mummified, stillborn, and weak newborn piglets from multiple commercial piggeries alarmed biosecurity authorities.

It was declared a "communicable disease incident of national significance" by the federal government on March 4.

By that time, Australia's chief veterinary officer, Dr Mark Schipp, said JEV had been confirmed at 14 piggeries across NSW, SA, Queensland and Victoria.

Officials said on March 1 as JEV was spreading among piggeries "it is the first time the virus has been detected in southern Australia".

The outbreak has already caused 40 cases of human infection and led to five deaths.

Biosecurity officials had long feared JEV's arrival after five cases had been identified in far north Queensland between 1995 and 1998.

It was thought JEV-infected mosquitoes were blown over by cyclonic winds from Papua New Guinea.

No more cases were found after 1998 and officials believed the emergency was over.

That was until a 45-year-old woman from the Tiwi Islands, offshore from Darwin, fell ill and died in February 2021.

This early case was confirmed this week in a letter in the New England Journal of Medicine authored by a number of Australian experts from the NT Department of Health, Charles Darwin University and the Australian Centre for Disease Preparedness in Geelong.

It has now been confirmed the fatality was the first of this current outbreak although it took a year for the alarm to be raised more than 3000km to the south.

The Tiwi Islands woman sought treatment for "acute confusion and fever".

She was admitted to Royal Darwin Hospital, placed on a ventilator in intensive care and died 15 days later.

Post-mortem tests have now confirmed the virus was "closely related" to the 2022 southeast Australian outbreak in samples taken from pigs, humans and mosquitoes.

Researchers say "possibilities" for the cause of this latest outbreak include JEV-infected mosquitoes which may have been wind-blown or caught a lift on planes or ships.

It may also have been transmitted to local mosquitoes from a JEV-infected migratory bird.

Experts believe infected water birds quickly spread the virus to the south "followed by virus amplification in commercial, domestic, and feral pigs".

Officially, like the dog disease ehrlichiosis it remains a mystery how it got to mainland Australia.

"It is likely that the movement of infected mosquitoes or migratory waterbirds may have played a part in the virus' spread," remains the official explanation.

The tick-borne ehrlichiosis was first detected in May 2020 in the far north of Western Australia.

It has now been found in all other mainland states.

Analysing the virus found infecting the Tiwi Islands victim, researchers say it closely matched samples taken from JEV-infected animals last summer, as well as a strain of the virus found in Indonesia.

The researchers say more sampling of these animals is needed to know whether we should expect another outbreak this summer.

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Those experts say the identification of JEV in Australia has many analogies to the outbreak of West Nile Virus in the United States.

That virus is also mosquito-borne and has caused more than 7000 human cases and more than 300 deaths in California since 2003.

The letter's authors said it was "worrisome that JEV may become endemic in Australia".