Extremely Effective Antibiotic Offers Hope For Koalas With Chlamydia


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

healthy koala

This koala's good posture and interested expression suggests it doesn't have chlamydia, or has been successfully treated, something that is now easier to do. nattanan726/

Despite all the competition from other strange and adorable creatures, koalas hold a special place in the hearts of Australians, and visitors. Unfortunately, they face threats to their survival in the wild from an abundance of directions, including the spread of chlamydia. The good news is that the common antibiotic doxycycline turns out to work exceptionally well in sick koalas, substantially exceeding known alternatives. Although habitat preservation and vaccination are key to koala survival, many koalas are already being saved by this treatment.

Chlamydia is wreaking havoc on koala populations, sending animals blind and inducing soggy bottom disease, which is as bad as it sounds. Animals in intact habitat can resist the bacterium, Dr Rosemary Booth of the Australia Zoo Wildlife Hospital told IFLScience, but in combination with other stressors, the disease is deadly.


More than 2,000 sick koalas have been brought to the hospital in the last five years, 46 percent with chlamydia. Sick koalas slumping while asleep lose enthusiasm for feeding, and eventually can't even climb trees.

Treatment is not as simple as for humans, Dr Booth added. Besides being infected by a different member of the chlamydia genus from us, koalas depend heavily on their gut bacteria to digest their unique diet, making some antibiotics lethal. Moreover, since koalas can't check themselves into clinics at the first symptoms, Booth seldom sees them until the infection has turned chronic.

For years chloramphenicol was the antibiotic of choice for treating koalas, but side effects in humans largely halted its production. Pharmaceutical company Seva provides the Wildlife Hospital with stocks every few years, but Booth wanted something more stable.

Booth used US Centers for Disease Control and Prevention (CDC) reports to find the antibiotics most frequently prescribed for human chlamydia and tested them on 86 koalas, some housed in the famous John Oliver Koala Chlamydia Ward.


Booth's results have been published in PLOS ONE. The study was not entirely randomized. For example, the paper notes, “Animals allocated to the doxycycline treatment group included the more aggressive or anxious koalas because this drug had the lowest dosing frequency.” Some drugs proved so obviously harmful to the koalas Booth dropped them from the trial quite early on. “The ethics were more important than the science,” she told IFLScience. "I'm not in the business of making koalas sick.”

The aggression paid off for some koalas, because it turned out doxycycline was the drug to get, curing 97 percent of those that received it. Chloramphenicol was next best with 81 percent.

Word spread to other koala treatment centers even before publication so koalas nationwide are already benefiting from Booth's work. However, she stressed to IFLScience the only thing that will save koalas long-term is the preservation of habitat with koala corridors to allow populations to mix. In the medium term, she holds hope for a vaccine. We all know the feeling.