Why do some koalas die from chlamydia and an AIDS-like retrovirus whereas others manage to avoid contracting the sexually transmitted diseases? The answer, it seems, may be in the genes. Scientists in Australia announced last week that they have sequenced the koala interferon gamma (IFN-g) gene, a discovery that they call the "holy grail" for understanding the koala immune system. A similar gene in humans helps to combat viruses and regulate the immune system.

The discovery could not come at a more important time for the species. About half of Australia's koalas (Phascolarctos cinereus) are infected with chlamydiosis (aka chlamydia), a disease caused by the chlamydia bacterium that can cause infertility, urinary and respiratory infections, blindness and death. Chlamydia is dangerous enough on its own but it has become even deadlier with the spread of the immunity-compromising koala retrovirus (KoRV). Australia finally listed koalas as a threatened species at this time last year following two decades of population losses.

Koalas have been worst hit by the diseases in the states of New South Wales and Queensland, where at least 40 percent of the animals have died since 1990. Some areas have been harder hit than others: In one area of South West Queensland koala populations have actually dropped by more than 80 percent due to a combination of drought and the STDs. Feral pests such as dogs, foxes and pigs have also preyed heavily on koalas, which have lost large portions of their forest habitats to human development. (The species is more vulnerable to attack when they are not in trees.)

Oddly, koalas in the state of Victoria have remained relatively unaffected by the chlamydia outbreak. Scientists want to find out why. "We know koalas are infected with various strains of chlamydia, but we do not know why some animals go on to get severe clinical disease and some do not," Queensland University of Technology (Q.U.T.) professor Peter Timms said in a prepared release about the IFN-g discovery. "We also know that 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 in understanding and controlling diseases in this species."

Following the discovery of the koala IFN-g gene, the Q.U.T. team has also developed a molecular test that allows them to measure the gene's expression in koala blood. By measuring that indicator, the researchers say they will better understand koalas' immune response, which could lead to treatments for infected koalas and even immunization against future infections.

Meanwhile the project to fully map the koala's genome continues, an effort the team says could help other threatened species such as Tasmanian devils, which are threatened with a communicable cancer. Scientists at Q.U.T. and the Australian Museum have so far identified 12,000 koala genes out of an estimated 20,000. They say they may need an additional $5.2 million in funding over the next five years to complete their work.

Previously in Extinction Countdown:

Photo by Stephen Young. Used under Creative Commons license