Antibodies to the virus, thought to have been passed from pigs to humans, perhaps via mosquitoes, have been found in the bats by Australian researchers, raising the possibility that they may be the original "reservoir" for the disease.

Some scientists believe that bats may also be the source for the killer Ebola virus.

New Scientist reports that more than 300 blood samples have been taken from bats throughout Malaysia.

In some areas, as many as a quarter of them show signs of contact with the virus.

Bats have been blamed for the outbreak

However, the conclusive proof - the presence of the virus itself - has not yet been found, although further tests are being carried out in the US on bat tissue.

Scientists now hope the lethal outbreak will produce funding to allow testing of bats throughout south-east Asia.

Peter Young of the Queensland Animal Research Institute said: "We want to check bats from the Philippines, Indonesia, Malaysia and Papua New Guinea."

The virus, called Nipah, is different from Japanese encephalitis, which can also be contracted in the region.

The Malaysian authorities have killed up to a million pigs in an attempt to control the spread of the new virus.

Brain swelling

Travellers to South East Asia between May and September are warned to take precautions against Japanese encephalitis.

The disease begins like flu with headache, fever, and weakness.

Gastrointestinal problems, including vomiting, as well as confusion and delirium may also be present.

In about one of every 200 cases, the illness progresses to inflammation of the brain, with more than half of those cases ending in permanent disability or death, which kills one in three of those infected.

This virus is thought to be transmitted by mosquitoes, and causes an inflammation or swelling of the brain.

A vaccine for Japanese Encephalitis has been available since the 1950s.

The current research was triggered by a related outbreak in Queensland, Australia, in 1994, which killed two.