The outbreak of Japanese encephalitis (JE) is now impacting four states as public health officials work to contain it.
Since the potentially fatal mosquito-borne virus was first detected near the New South Wales-Victoria border last week, cases have been recorded in Queensland and South Australia.
A Department of Agriculture, Water and the Environment spokesperson said three cases of Japanese encephalitis had been confirmed in humans, and a number of possible cases were under investigation.
The spokesperson said it was anticipated that more cases would be confirmed shortly.
Australia's Chief Veterinary Officer Mark Schipp said animals at 21 piggeries had been infected.
"We're mapping the presence of waterbirds, feral pigs or piggeries and people that have contracted the infection," he said.
There is a vaccine available as well.
"That's the purpose of the mapping that we're undertaking at the moment — to prioritise those vaccinations and then rolling the vaccinations out further from there," Mr Schipp said.
The movement of pigs on farms with positive cases is being restricted.
Pork SA chairman Andrew Johnson is urging pork producers to report suspected cases.
"Farmers that see any symptoms, they shouldn't be afraid to advise accordingly," he said.
JE cannot be transmitted to humans by eating pork products and producers will still be able to transport livestock to abattoirs.
"If there's a suspect case, or if there is a positive case, those farms will be issued a movement permit that will allow them to continue business," Mr Johnson said.
Mosquito-borne virus
The virus is transmitted by mosquitoes and cannot be passed from livestock to humans.
"Japanese encephalitis is a virus carried by mosquitoes from water birds or pigs to humans or horses," Mr Schipp said.
"Pigs are an amplifying host, so they produce a lot of virus and the mosquitoes pick that up and carry it forward into humans and horses."
JE is not normally found in Australia and health officials survey the Torres Strait and the Top End every year to check for outbreaks.
This outbreak has been found along the Murray River corridor.
Mr Schipp said it was surprising to find JE so far south.
"It will have a large impact on human health and industry," he said.
"The impacts on tourism, for example, could be significant.
