The Ross River virus risks becoming a global epidemic on the same scale as the Zika virus, Australian researchers say.

An Australian National University and University of Adelaide study has found that Ross River transmitted by mosquitoes could be carried by all mammals and not just kangaroos and wallabies as previously thought.

"The traditionally accepted thinking and all evidence points to the fact that the virus needs a marsupials reservoir - so when kangaroos and wallabies are around - and it then gets picked up by a mosquito which then transmits it to humans," University of Adelaide professor Philip Weinstein told AAP.

"What the new research shows is that it can do this without the marsupials ... you could have dogs, cats and rats playing the role that we thought only marsupials could do."

While the virus is currently confined largely to Australian and Papua New Guinea, Prof Weinstein says it's "probably a question of when, not if" Ross River virus spreads further afield, in the same way the Zika virus was transmitted.

Zika, spread by infected mosquitoes, can infect a foetus and cause birth defects.

The findings on Ross River come after blood tests from American Samoans who had never left home revealed exposure to the virus.

This pointed to the transmission of the virus after the 1979-80 epidemic, which was thought to have died out.

As there aren't any marsupials in American Samoa, Prof Weinstein said it was only reasonable to conclude that the virus could circulate in local mammals.

"If RRV can circulate in non-marsupials in the South Pacific, then it can find a home anywhere in the world," he said.

"There are tourists travelling all the time from Australia, some of whom will carry the (Ross River) virus. If that can start an epidemic in another country, that can take off and become a global epidemic."

The condition isn't deadly but causes fever, joint pain, rashes, lethargy and can be debilitating.