Scientists Begin Vaccinating Wild Koalas Against Chlamydia

The effort is part of a field trial to limit the debilitating bacterial disease that can cause infertility, blindness and death

Two koalas in a tree
Vaccinations of wild koalas began in March this year. For now, scientists hope to inoculate 50 individuals. Martin Harvey via Getty Images

Scientists in Australia have begun capturing and vaccinating wild koalas against chlamydia, a debilitating disease that can lead to blindness, infertility and death in the marsupials, reports Christina Larson for the Associated Press. The vaccines, which are being delivered as part of a scientific trial, are an experimental solution for the animals’ plight.

Cases of chlamydia have risen dramatically in recent years, with half of all wild koalas in the state of Queensland believed to be infected. 

“It’s killing koalas, because they become so sick they can’t climb trees to get food or escape predators,” Samuel Phillips, a microbiologist at Australia’s University of the Sunshine Coast who helped develop the vaccine, tells the AP. 

Chlamydia is caused by bacterial parasites that infect hundreds of species, including amoebae, insects, aquatic animals, reptiles, birds and mammals. In humans, the bacterial strain Chlamydia trachomatis causes one of the most common sexually transmitted infections in the world, with about 131 million people infected every year. Antibiotics can generally cure chlamydia in humans, but for koalas, treatment is much trickier. 

Giving these drugs to koalas can mess with their unique gut bacteria that allow them to digest eucalyptus leaves. And reinfection is common: “In a lot of cases, if you just treat them with antibiotics, they often come back with chlamydial disease again,” Peter Timms, a microbiologist at the University of the Sunshine Coast, told the Guardian’s Donna Lu in 2021. The disease spreads between the animals both sexually and from mother to child.

Over the past decade, Timms, Phillips and their colleagues have been developing a protein-based vaccine against chlamydia that has already been tested in hundreds of koalas in wildlife rescue centers in Australia. This March, the first wild koalas were caught, vaccinated, monitored and marked with pink dye on their backs so they wouldn’t be captured again, per the AP.

The scientists plan to vaccinate half of the koala population in the Northern Rivers region of New South Wales, or about 50 individuals. The vaccine will not cure a koala of chlamydia, but the team hopes it can lower the animals’ infectiousness enough to slow the spread. With this trial, the team wants to find out how much of a wild population they must inoculate to significantly reduce cases. 

But chlamydia isn’t the only threat koalas are facing—climate change and bushfires have led to populations being “chronically stressed,” Timms told CNN’s Ben Westcott in 2021. 

“All that leads to poor chlamydia response. It gets them from low grade chlamydia infections to more serious disease,” he told the publication. “That’s what we’re doing to them. And we’re doing it on all fronts.”

The Australian Koala Foundation estimates that less than 57,920 koalas are left in the wild—and possibly as few as 32,065. Last year, Australia declared koalas endangered in some eastern parts of the country. 

Though widespread vaccinations of wild animals aren’t unheard of, they’re “certainly not routine yet,” Jacob Negrey, a biologist at Arizona State University, tells the AP.

One of the most well-known vaccination campaigns for wildlife in the U.S. might be the oral rabies vaccine, which began nationwide in 1997. The U.S. Department of Agriculture has since airdropped millions of vaccine packets in locations for coyotes, foxes and raccoons to consume. In Brazil, scientists are currently vaccinating wild golden lion tamarins against yellow fever. 

“Vaccination is an incredibly resource-intensive thing to do,” Rebecca Johnson, chief scientist at the Smithsonian’s National Museum of Natural History who previously led the Koala Genome Consortium in Australia, tells the AP. “But because the effects of chlamydia are so debilitating, I think it’s totally worth it.”

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