Trial begins to test koala-ty of chlamydia vaccine

Scientists have begun an ambitious field trial in New South Wales, vaccinating wild koalas against chlamydia.

Many of us have grown up hearing the “fun fact” that 90 percent of koalas have chlamydia. But this is no laughing matter. The disease has spread dramatically among koalas since the 1990s and can have deadly consequences.

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Actual infection levels vary in different populations. It is believed that half of all wild koalas in Queensland are infected. In some populations, up to 100 percent of individuals are believed to be infected with the sexually-transmitted disease.

A 2018 study of nearly 300 dead koalas found that 18 percent of the deaths were attributable to chlamydia.

“It’s killing koalas because they become so sick they can’t climb trees to get food, or escape predators, and females can become infertile,” University of the Sunshine Coast microbiologist Dr Sam Phillips told Associated Press.

The new trial aims to catch, vaccinate and monitor around half the koala population in the Northern Rivers region of New South Wales – roughly 50 animals. The first koalas were caught in March, and the trial is expected to last three months.

The single-shot vaccine is specifically designed for koalas and has already been tested by vaccinating hundreds of koalas brought to wildlife rescue centres for other reasons.

Now scientists want to understand the impact of vaccinating wild koalas.

Koalas are given a check-up make sure the animals are in good condition before being given an anaesthetic and the vaccine. They are then kept for observation for 24 hours after they wake up to confirm there are no unexpected side effects.

“We want to evaluate what percentage of the koalas we need to vaccinate to meaningfully reduce infection and disease,” Phillips says.

Their goal is to vaccinate healthy koalas to prevent chlamydia infection.

Inoculated koalas are given a pink dye patch on their backs to prevent being caught twice.

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It is not clear what has caused the chlamydia epidemic in koalas. But scientists believe the marsupials initially caught the disease after exposure to the faeces of livestock brought from Europe in the 19^th century.

Chlamydia then spreads through the koala population either sexually or is passed from mother to offspring.

The disease is caused by bacteria and can infect hundreds of different species.

In humans, Chlamydia trachomatis causes one of the most common sexually-transmitted diseases. The World Health Organisation estimates about 131 million people are infected every year. But this can be treated and cured in humans with a simple course of antibiotics. Not so for koalas.

Koalas are highly specialised eaters, feasting almost solely on eucalyptus leaves. A complex array of microbes in the koalas’ stomach help neutralise the toxins in the leaves. But this also leads to the neutralisation of some medicines, meaning koalas don’t respond well to antibiotic treatments.

The use of vaccination among wild populations of animals is not yet widespread. It is resource-intensive and requires high levels of human intervention.

But, the benefits may outweigh the risks when it comes to defending the beloved marsupials.