A VACCINE for the deadly Hendra virus has been tested on cats but it will take at least five years to determine its suitability for humans, researchers say.

Dr Deborah Middleton, an animal biosecurity expert at the Australian Animal Health Laboratory in Geelong, said a potential vaccine for the related Nipah virus appeared to be able to combat Hendra virus.

"We've got some preliminary data that shows protection against disease in cats," she said.

A five-year research program could produce a vaccine suitable for humans.

She said the vaccine was being tested on laboratory ferrets as a more suitable model.

There have been three human deaths linked to Hendra virus since it was first isolated in 1994.

The last major outbreak, in July at the Brisbane bayside Redlands Veterinary Clinic, killed vet Ben Cunneen.

Five horses at the clinic either died or were put down after contracting the virus, believed to have been transmitted by bats.

Another three horses were put down in a separate outbreak in north Queensland in August.

The research was a topic of discussion at a gathering of more than 100 people at an Australian Association for Veterinary Laboratory Diagnosticians forum in Brisbane yesterday.

Principal epidemiologist with the Queensland Department of Primary Industry, Hume Field, said the search to find out how the deadly Hendra virus was spread has narrowed to two of the four species of flying fox in Australia.

"It may be that two of the four flying fox species are more dangerous than others," Field said.

He said the range of the black flying fox and the little red flying fox overlap with the 11 cases of infection, implying they carried the disease.

Field said research also indicated the chance of the disease affecting horses and humans was more likely during the reproductive season and food shortages.

Queensland's chief veterinary officer, Dr Ron Glanville, said while there were no known cases of humans catching the disease from flying foxes, people should be careful handling them.