Genome the blueprint for saving koala

Chlamydia in fatal combination with an HIV-type virus is spreading through Australia's koalas. Photo / Sarah Ivey
Chlamydia in fatal combination with an HIV-type virus is spreading through Australia's koalas. Photo / Sarah Ivey

A year ago the koala, Australia's iconic marsupial, was officially listed as a threatened species in large parts of the country after two decades of devastating population losses.

Hard hit by drought, habitat loss and attacks by other animals including domestic dogs, Australia's koala population has also been ravaged by disease, including a sexually transmitted strain of chlamydia and the koala retrovirus (KoRV) - their equivalent of HIV - often found in disastrous combination.

But now, Australian researchers have announced what they describe as the discovery of the "holy grail" for understanding the workings of the species' immune system, raising the prospect that the diseases might be better controlled with vaccines and the koala saved from extinction.

Koalas, the world's largest tree-dwelling marsupial, hunted almost to extinction in the 1920s for their fur, eat only the leaves of eucalyptus trees and spend much of their time sleeping. The current population, numbering 100,000 animals at most, represents the only surviving representative of the family Phascolarctidae, after the extinctions of several other koala species over the last 15 million years.

In southwest Queensland, once home to Australia's largest inland koala population, disease and other factors have caused numbers to drop from an estimated 60,000 in 1990 to 11,000 last year. Some 4000 koalas are dying annually nationwide.

The increased pace of research follows a 2011 Australian senate inquiry which recommended new funding for research, including vaccination programmes.

Last week the Australian Museum and the Queensland University of Technology announced they had succeeded in mapping the koala's genome, including the interferon gamma (IFN-g) gene - the chemical messenger that plays a key role in managing the animal's defences against cancer, viruses and intracellular bacteria. Much of the genetic material that was analysed came from a single koala known as Birke, who was put down after a dog attack.

"We know koalas are infected with various strains of chlamydia, but we don't know why some animals go on to get severe clinical disease and some don't," said lead researcher Professor Peter Timms.

"We also know genes such as IFN-g are very important for controlling chlamydial infections in humans and other animals. Identifying these in the koala will be a major step forward."

The koala retrovirus, first identified in 2000 and suspected of triggering both cancer and an Aids-like disease, is spreading south to islands where there is the lowest incidence. Almost all koalas test positive for KoRV in the north.

But recent analysis on DNA samples sequenced from koala skins in museums suggests the disease was already prevalent 120 years ago.

"By analysing this information we should be able to determine if KoRV is sitting harmlessly in these koalas or if it's potentially triggering cancer or resulting in mild chlamydia infections becoming a serious clinical disease," Timms said.

Mapping the koala genome is the first step in understanding why the animal is so vulnerable to the two sexually transmitted diseases, and why some population groups are worse afflicted than others. While southwest Queensland has lost 80 per cent of its koalas, in Victoria chlamydia is uncommon. According to some estimates, about half of all Australia's koalas are infected with a strain of chlamydia which can cause infertility, as it does in humans, as well as urinary and respiratory infections and blindness. Data from the genome project accelerated efforts to develop and start trialling chlamydia vaccines. These are being given to koalas brought into animal welfare centres.

Observer

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