These Are The Last Koalas Without Chlamydia

Kangaroo Island, off the coast of Southern Australia, may be the only place on Earth with a koala population free of chlamydia.
Koala with an open mouth
John Milner/SOPA Images/LightRocket via Getty Images

Chlamydia has infected nearly every koala population, threatening the safety of the entire species. Now, there may only be one place on Earth where koalas are safe from the disease: Kangaroo Island in Australia.

While Northern Australia koalas have been hit hard by chlamydia, researchers thought that the two largest populations in Southern Australia—Kangaroo Island and the mainland Mount Lofty Ranges (MLR)—appeared less affected. If really healthy, these populations could provide hope for the future of the koala species.


To test that theory, researchers from the University of Adelaide caught koalas from Southern Australia and swabbed them, looking for DNA from Chlamydia pecorum bacteria.

All 170 koalas from Kangaroo Island had no sign of chlamydia infection, the researchers said in a study published in Nature’s Scientific Reports. To be sure, the researchers analyzed historic data from over 13,000 koalas from Kangaroo Island over a 22-year period, finding no signs of chlamydia.

In the MLR population, though, the chlamydia bacteria was still common. Nearly half the koalas of the 75 koalas sampled were infected with chlamydia bacteria, but only 4 percent had the clinical disease.

While not always escalating to the level of disease, the infection appeared to seriously reduce koala fertility. None of the reproductively active females in MLR were positive for chlamydia, while nearly all of the reproductively inactive females had the infection.

Chlamydia has devastated nearly every known koala population. The disease, spread through sexual contact or from mother to joey, causes widespread infertility, blindness, pneumonia, urinary tract infections, and can ultimately be fatal. In Northern Australia, more than 20 percent of koalas have chlamydia, with many more harboring the infection.

Researchers have been largely unable to fight the spread of this disease, as koalas need to receive antibiotics from wildlife hospitals. With infection rates so high, it’s nearly impossible to treat every koala, and the antibiotics may be alter the specialized gut microbes koalas use to digest eucalyptus, according to previous studies.

As more populations decline as a result of chlamydia infections, the Kangaroo Island population could prove invaluable as a breeding population. Koalas are classified as “vulnerable” under the International Union for Conservation of Nature (IUCN) Red List. This last large, chlamydia-free population could be the best hope koalas have at rebounding.