Link: https://www.theguardian.com/environment/2026/oct/26/koalas-australia-chlamydia-vaccine

At wildlife hospitals across eastern Australia, many koalas brought in have distinctive brown patches on their bottoms – a sign of urinary incontinence and a painful inflamed bladder. Others have red, weeping eyes, pointing to a bacterial disease that can cause blindness in the endangered marsupials.

Chlamydia infection, also known as chlamydiosis, is the most significant disease affecting the animals. The culprit is most commonly the bacterium Chlamydia pecorum, which is spread via mating or close contact.

“Relatively inevitably, infected females will become infertile, and quite rapidly,” says Mark Krockenberger, a professor of veterinary pathology at the University of Sydney.

Dr. Freya Russell, a postdoctoral research fellow at the Queensland University of Technology (QUT), adds: “In the animals that are heavily diseased with chlamydia, they can also be quite emaciated too … more boney rather than the robust kind of koala we’re used to seeing.”

Infection rates vary geographically, but in some koala populations the prevalence of chlamydia is as high as two in three. Populations in northern regions tend to be worse affected than those in the southern states.

Researchers have struggled for years to devise a solution to bring koala chlamydia rates down. Two separate chlamydia vaccines have been in development in Queensland for more than a decade. One was approved by the veterinary medicines regulator last year, but questions have been raised about its efficacy. What will it take to save the iconic animal from one of its key existential threats?