The Japanese encephalitis virus has been discovered among feral pigs for the first time.
Now the virus is confirmed in the wild, experts say it is another indication JEV will likely be declared endemic in Australia.
The mosquito-borne disease first caused alarm as it quickly spread among domestic piggeries across Australia when first detected in February.
A total of 35 people have so far been confirmed with the virus from around Australia with three deaths.
There are more than 50 infected piggeries in Victoria, South Australia, Queensland and NSW.
The Northern Territory government has confirmed a feral pig from the west Daly region tested positive for JEV last month.
A government spokesman said at least one pig tested positive in mid-March as part of a routine animal health survey conducted by the Northern Australia Quarantine Strategy.
Further surveys and testing of feral pigs, horses and other animals for JEV are continuing.
An Alpaca in South Australia has also tested positive, but like horses it is considered a "dead-end" host meaning it does not spread further.
The animal was in the Adelaide Plains council area.
The virus has now been found in six commercial piggeries in South Australia - Clare and Gilbert Valleys, Goyder, Loxton Waikerie, Murray Bridge and Coorong local government areas.
The outbreak has spread to another Victorian piggery in the past week.
There is now a total of 19 properties with pig cases across the Wangaratta, Moira, Greater Shepparton, Campaspe, Gannawarra, Loddon, Greater Bendigo and Northern Grampians local government areas.
A number of suspected cases are under investigation.
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The human cases of JEV in NSW are from Balranald, Berrigan, Federation, Goulburn Mulwaree, Griffith, Temora and Wentworth.
The virus has been confirmed at piggeries in the Forbes and Wagga Wagga regions.
Queensland has two confirmed human cases of JEV, several suspect cases and just a few infected piggeries in the south of the state.
There is no risk to humans from eating pork with health authorities encouraging people in at risk areas to cover up to prevent bites from mosquitoes.
Vaccines are recommended for people at a higher risk of exposure to the virus, such as those working with pigs.
The Federal government is spending almost $30 million buying more vaccines from across the world - enough for about 130,000 doses for priority groups.
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