New vaccine could protect koalas from deadly chlamydia infection

Since this year, in the Netherlands, you can no longer get tested or treated for the relatively harmless chlamydia if you don't have symptoms. However, a thoroughly tested and approved vaccine is now available for koalas. For the endangered native Australian species, the sexually transmitted bacterial infection is often fatal, unlike in humans. In fact, the vaccine is intended to save the marsupial from extinction.

Koalas are particularly susceptible to chlamydia. Both males and females can have it and transmit it, both through mating and nursing. They develop nasty urinary tract infections, conjunctivitis (eye inflammation) leading to blindness, become infertile, and can eventually die from the bacterial infection—or from starvation. It's thought that 50 percent of deaths are due to the bacterial infection.

Population is plummeting

For over a decade, the research team at the University of the Sunshine Coast has been working on the vaccine, hoping to halt the bacterial infection that's causing the population to plummet. In some colonies, particularly in New South Wales and Queensland, there are even "infection rates as high as 70 percent," microbiology professor Peter Timms told the BBC. "And they're creeping ever closer to extinction."

The infected koalas have been treated with antibiotics until now, but even that was not without risks. The koala's diet consists almost exclusively of eucalyptus leaves. These leaves are full of toxic molecules, but thanks to special enzymes in the liver and bacteria in the intestines, koalas can still digest them—without getting high. However, the antibiotics disrupt this unique defense mechanism against the poison, making it more difficult for them to digest these leaves. This, in turn, can lead to starvation.

The vaccine could reduce deaths by 65 percent, but that's not enough, Timms told the BBC. "The other factors also need to be addressed." Habitat loss due to urbanization and agriculture, and natural disasters like wildfires, aren't helping either. "But the most important thing is habitat loss," Timms said. "If you don't have a tree, nothing else matters much."

The koala has been officially listed as an endangered species by the Australian government since 2022. An estimated 50,000 koalas currently live in Australia, but certain colonies could disappear entirely due to chlamydia – even within a single generation.

The vaccine, as well as the restoration of their natural habitat, should ensure that the koala not only survives but thrives, writes Australian Environment Minister Murray Watt on his website. This week, the state of New South Wales announced the addition of 176,000 hectares to the existing Great Koala National Park.

Forked penis

There, hopefully aided by the vaccine, the koala can begin working towards population recovery. And things look a little different for koalas. The female, who lives a comfortable single life for most of the year, searches for a male around December when the weather improves. Only after mating does an egg release – just like in rabbits, camels, and cats. This way, no eggs are wasted on monthly ovulation, as in humans.

Even more remarkable is that male koalas, like most marsupials, have a forked penis. Females have a single orifice, but it branches into three vaginas. It's suspected that one is related to the other.

What researchers in Australia do know, however, is that funding is needed to roll out the vaccination program. The cost of locating, capturing, and vaccinating is estimated at 7,000 Australian dollars (3,959.65 euros) per koala. Nevertheless, Timms hopes they can start administering the vaccinations free of charge. And preferably as soon as possible, because even without chlamydia, koalas face "numerous life-threatening threats." The vaccine would eliminate at least one of those threats.