‘Devastating’: Australian scientists race to save endangered wild koalas from chlamydia

Wild koala populations are being devastated by chlamydia.
Wild koala populations are being devastated by chlamydia. Copyright canva
By Ruth Wright with APTN
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“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”


Australian scientists have begun vaccinating wild koalas to boost a declining population.

“It’s been devastating - there’s very, very low fertility," says Mathew Crowther, a conservation biologist at the University of Sydney says. "You hardly see any babies.”

But it’s not COVID this time. The ambitious field trial will protect koalas against chlamydia which can cause them to become blind, infertile, or even die.

“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,” says Samuel Phillips, a microbiologist at the University of the Sunshine Coast who helped to develop the vaccine.

What's the link between wildfires and chlamydia?

The other threats koalas face - including habitat destruction from land clearing and climate-enhanced wildfires - may increase their stress levels, weakening their immune systems and making them more susceptible to diseases including chlamydia, says Crowther.

The scientists’ initial goal is to catch, vaccinate and monitor around half of the koala population in the Northern Rivers region of New South Wales - that means vaccinating around 50 animals.

Around half of wild koalas in Queensland are already infected with chlamydia, scientists estimate.

The safety and effectiveness of the single-shot vaccine, which has been designed specifically for koalas, has previously been tested by vaccinating a few hundred koalas brought to wildlife rescue centres for other afflictions.

Now scientists want to understand the impact of vaccinating a population of wild koalas. “We want to evaluate what percentage of the koalas we need to vaccinate to meaningfully reduce infection and disease,” says Phillips.

Are koalas an endangered animal?

Koalas are iconic Australian marsupials, like wombats and kangaroos. They spend most of their time eating and sleeping in eucalyptus trees, and their paws have two opposing thumbs to help them grasp and climb up trunks.

Australia's wild koala populations have declined steeply in the past two decades.

Last February, Australia’s federal government declared koalas “endangered” in the eastern regions of New South Wales, Queensland and the Australian Capital Territory.

Facing compounded threats from disease, habitat loss and road collisions, koalas could become extinct by 2050, according to a 2020 assessment from the New South Wales government.

How scientists vaccinate wild koalas

Researchers use binoculars to spot koalas in eucalyptus trees, then construct circular enclosures around the tree bases with doors leading into cages.

After a few hours or days, the koalas will eventually climb down from one tree to seek tasty leaves on another, and wander into the harmless traps.

“It's hard to confuse a koala with any other animals - they're pretty easy to spot,” says Jodie Wakeman, veterinary care and clinical director at Friends of the Koala, a non-profit that runs a wildlife hospital where the koalas are being brought for vaccination.

After a check-up to make sure the animals are in good condition, researchers administer anaesthesia and shots of vaccine, then keep them under observation for 24 hours after they wake up to confirm there are no unexpected side effects, says Wakeman.

The goal is to vaccinate healthy koalas to prevent them from becoming infected with chlamydia.


Before release, the researchers mark the koalas with a dab of pink dye on their backs, to ensure the same animals aren’t caught twice.

When the first vaccinated koala was returned to her habitat in March, the scientists placed her cage at the base of a tree and opened the door. She quickly emerged and bounded up the tree trunk.

How do koalas catch chlamydia and can it be cured?

In deciding to vaccinate, the scientists are balancing the risk of disturbing the animals against the danger of allowing the disease to spread. The trial was approved by multiple government bodies, including Australia's agriculture department and New South Wales' planning and environment department.

The origins of chlamydia in koalas aren’t confirmed, but scientists believe it’s likely the marsupials initially caught the disease from exposure to the faeces of infected sheep and cattle. Then it's spread sexually or passed from mother to offspring.

While humans and livestock infected with the bacteria that causes chlamydia can be treated with antibiotics, it’s not so simple for koalas.


The “complex” microbes inside the stomachs of koalas are designed to neutralise toxins in eucalyptus leaves that are their main food source, says Crowther, a conservation biologist at the University of Sydney. But their digestive systems can also neutralise some medicines so “that means they don’t respond well to antibiotics treatment," he says.

Will vaccinating wild animals become more common?

There are only a handful of other examples worldwide of scientists attempting to catch and inoculate endangered wildlife for conservation. In 2016, scientists began to vaccinate Hawaiian monk seals against a deadly strain of morbillivirus. Two and a half years ago, biologists in Brazil began to vaccinate golden lion tamarins against yellow fever.

“Vaccination for wildlife is certainly not routine yet,” says Jacob Negrey, a biologist at Wake Forest University School of Medicine. “But whether it should be used more often is a fundamental question that conservation biologists are really wrangling with right now.”

The Smithsonian's Johnson says the benefits are likely to outweigh the risks for koalas. “Vaccination is an incredibly resource-intensive thing to do. Koalas live high up in trees," she says.

“But because the effects of chlamydia are so debilitating, I think it’s totally worth it.”

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