AIDS-like virus new threat to koala

A virus that may weaken the immune system of koalas, similar to HIV in humans, is a new “wild card” among threats facing the species and nearly all koalas in Queensland could already be infected.

Discovered in 2000, the retrovirus is the latest in a series of threats facing the iconic marsupial, which include the sexually-transmitted infection chlamydia, habitat fragmentation, collisions with vehicles and the impact of feral animals.

KoRV (koala retrovirus) integrates itself into the animals’ DNA, and may be passed on genetically as well as through direct infection, experts have found, though they are unsure how it is spread. The virus evolved only 100 to 200 years ago, according to a study published in the journal Nature in 2006.

This study showed that "100 per cent of all animals tested in Queensland and north of Sydney have the retrovirus, but in Victoria and the southern states it seems to be less prevalent," said Damien Higgins of the Koala Infectious Disease Research Group at the University of Sydney.

Fatal disorder?
 
Scientists do not yet know if the virus weakens the immune system enough to develop into a fatal AIDS-like disorder as a similar infection does in cats, Damien said.

The virus may leave afflicted animals at greater risk of other diseases, such as cancer or chlamydia, which can render them infertile. According to molecular biologist Peter Timms from the Queensland University of Technology in Brisbane, 40-70% of koalas currently test positive for chlamydia, with 10-25% of them showing symptoms at any one time.

He recently conducted a study of 100 koalas in conjunction with researchers at the University of Queensland and the Australian Wildlife Hospital in Beerwah to find out if KoRV-infected koalas experience greater levels of chlamydia.

The results are yet to published, but the association between the two diseases wasn’t as marked as expected, Peter told Australian Geographic. He still believes there may be a link, however. "Chlamydia will cause infections in healthy animals but if you have an immune-suppressed animal you would logically think it would get more infections and more disease," he said.

While chlamydia presently poses a more significant threat, the retrovirus is nevertheless spreading through the koala population which is of some concern, Peter said.

Ups and downs

Wildlife ecologist Kath Handasyde, from the University of Melbourne, is the co-author of a chapter on koalas in the book Mammals of Australia. She emphasised that koalas are not threatened with extinction and at this stage have not been classified as vulnerable by the Australian Government.

"Reports of extinction are greatly exaggerated," Kath said. "[But] the retrovirus is a wild card so we do need to be vigilant." Some populations are declining, while others are increasing, but the animal is distributed over a very large area, she said.

Peter warned that further unpublished research he has seen indicates that some koala populations showed a  significant decline. “There are local extinctions going on all the time – not just hundred but thousands of animals,” he said. “We need to study [populations] in more detail from all perspectives to find out what we can do from a management level.”

KoRV is a “very common virus and if it is causing the animals to be more susceptible to disease [such as chlamydia] it would be very threatening to the koala population,” warned Damien Higgins.