Koalas Have a Big Chlamydia Problem — but a New Vaccine Could Save Them

Koalas Have a Big Chlamydia Problem — but a New Vaccine Could Save Them
A baby koala is seen at the Wild Life Sydney Zoo on October 14, 2021 in Sydney, Australia. (Photo: Mark Evans, Getty Images)

A new experimental vaccine could put a serious dent in the widespread epidemic of chlamydia that has devastated populations of koalas. This month, scientists in Australia announced the start of a large clinical trial that will vaccinate hundreds of koalas against the bacterial disease, which also sickens humans around the world.

Chlamydia is caused by various species of Chlamydia bacteria, depending on the animal. In humans, the sexually transmitted infection can cause genital pain and discharge, though most infected people will experience no symptoms at all. If not treated with antibiotics, chronic chlamydia can also cause permanent damage to the uterus and infertility, as well as raise the risk of catching other sexually transmitted infections. Pregnant people infected with the bacteria are at higher risk of a premature delivery, and the infection can be passed down to the newborn during delivery, which can cause pediatric pneumonia and conjunctivitis.

As bad as chlamydia can be for humans, the koala version, which is caused by a different species of the bacteria, is more serious and widespread. The infection can be life-threatening to these animals, and even those that survive can be left with permanent bladder damage, blindness, and infertility. Estimates vary, but upwards of 50% of koalas are thought to carry the infection, which is also sexually transmitted or passed down from mothers to newborns. Though antibiotics can treat koala chlamydia, they can come with serious side effects and often aren’t a good option for koalas with poor pre-existing health.

Koalas have been already facing a population crunch in recent years, thanks largely to killer wildfires, and chlamydia hasn’t been helping matters. While there are ongoing efforts to develop better antibiotics for koalas, the holy grail for many scientists has been a chlamydia vaccine, one that could not only protect koalas but other livestock in Australia vulnerable to the same species of bacteria. And it seems we’re closer than ever to such a vaccine becoming a reality.

The new Phase 3 trial of this experimental vaccine is being led by researchers at University of the Sunshine Coast (USC) in Queensland, Australia. The single-dose vaccine will be doled out to 400 koalas that are admitted to the Australia Zoo Wildlife Hospital for other reasons. After their routine care, the koalas will be vaccinated before they go back into the wild. The vaccine has previously been tested in about 200 koalas, both captive and wild, with promising results. More trials are planned at other wildlife hospitals and rehabilitation centres, covering different regions of the country.

“While this vaccination will directly benefit each of the animals, the trial will also have a focus on the protection provided by vaccination,” said trial researcher Peter Timms, a microbiologist at USC, in a statement from the university. “All koalas will be microchipped and the hospital will record any animals that return for any reason over the following 12 months.”

While these trials are ongoing, the researchers are looking to partner up with a vaccine manufacturer to secure mass production, and they’re also working to get the vaccine registered by the Australian Pesticides and Veterinary Medicines Authority. If all goes well, koalas may have a widely available vaccine against chlamydia within a few years.