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Virus starts cancer in koalas

July 17, 2004

A VIRUS that jumped to koalas, possibly within the past 200 years, is responsible for the astonishingly high incidence of koala cancer, Australian researchers have found.

In a peculiar scientific twist, the virus is similar to those that trigger leukaemia in cats and gibbon apes.

The virus is not known in other marsupial species.

"The initiating factor is the viral infection itself," virologist Paul Young said yesterday.

"That leads to cancers like leukaemia and lymphoma and also to immune suppression and subsequent infections like chlamydia," said Dr Young, leader of the University of Queensland team that nailed the virus.

According to Dr Young and his colleagues, doctoral student Rachael Tarlinton and veterinary scientist Joanne Meers, fewer than 1per cent of humans die of leukaemia or lymphoma.

However, up to 70 per cent of captive koalas and 3 to 5 per cent of wild koalas die of cancer.

The killer virus - an endogenous gamma retrovirus called KoRV - was identified four years ago by another UQ group.

Dr Young and his colleagues then looked for the virus in 150 koalas, half of which were wild animals brought to clinics including Moggill Koala Hospital near Brisbane.

The remaining koalas live in the colony at Dreamworld on the Gold Coast, which helped fund the research.

Every koala tested positive for KoRV, which is inherited. But those with cancers and immunosuppressive diseases had high viral levels,

"What we're trying to do now is find if certain strains of the virus are more or less likely to cause disease, and try to select those animals for breeding or translocation programs," Ms Tarlinton said.

The findings were presented at DNA7, an international conference on ancient DNA in Brisbane this week.

The team also hopes to obtain DNA from historical koalas to pinpoint when koalas were first infected.

Because KoRV is so close to the gibbon virus, it is suspected that it jumped to both apes and koalas from another species.