Can you catch chlamydia from a koala?

You’ve probably heard that chlamydia is common in koalas, and it raises some fair questions: can we catch it from them, can they catch it from us, and does it affect koalas the way it affects people? Here are the facts, starting with what chlamydia actually is.

Understanding chlamydia

Chlamydia is a sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. It’s the most commonly reported STI in Australia, especially in people aged 15 to 29, with more than 100,000 notifications a year. It’s spread through skin-to-skin contact during vaginal, anal and oral sex, and can also pass on by sharing sex toys or genital-to-genital contact.

It’s often called a “silent infection” because most people with chlamydia have no symptoms, which makes it hard to diagnose and easy to pass on. When symptoms do appear, they can include:

• painful urination
• unusual or smelly discharge from the vagina, penis or anus
• pain in the abdomen, testicles or rectum
• pain during sex, or vaginal bleeding after sex
• redness at the opening of the penis, or conjunctivitis.

Left untreated, chlamydia can cause serious complications. In women it can lead to pelvic inflammatory disease, which may cause infertility, ectopic pregnancy or chronic pain, and it can be passed to a baby at birth; in men it can cause testicular pain, infertility or reactive arthritis. The good news is that it’s easily cured with antibiotics once found, which is why a simple chlamydia test matters. For the full picture, see our guide to the long-term risks of chlamydia.

Chlamydia and koalas

Koalas are also badly affected by chlamydia, but by different strains from the one that infects people. Koalas are mainly affected by Chlamydia pecorum and Chlamydia pneumoniae. These strains are a serious threat to koalas: in some regions, an estimated 90% of the local koala population may be infected.

That widespread infection is a major driver of falling koala numbers — koalas are listed as endangered across much of eastern Australia — and a real challenge for conservationists. Managing it means monitoring and treating infected animals in the wild, which is difficult, expensive and can only reach a fraction of the population, which is why a vaccine has been such an important goal.

Signs and symptoms of chlamydia in koalas

The signs in koalas are quite different from those in people. Some koalas have no symptoms, while others develop:

• conjunctivitis, which can cause blindness if untreated
• cystitis (a bladder infection), which can lead to incontinence
• infertility, which is a critical threat to the survival of the species.

Treatment is harder than in humans, too. Antibiotics that cure chlamydia in people can wipe out the gut bacteria koalas rely on to digest eucalyptus leaves, their only food, which can lead to starvation. The encouraging news is that in 2025, scientists at the University of the Sunshine Coast developed a koala chlamydia vaccine, which has been approved, with a rollout planned from 2026.

Can humans get chlamydia from koalas?

No. Although both species get chlamydial infections, the strains are different, so humans are not at risk of catching chlamydia from a koala, even with direct contact.

Can koalas catch chlamydia from humans?

No. For the same reason, koalas can’t catch the human strain from us. There’s no cross-species transmission in either direction, so conservation efforts can focus on the koalas themselves, and human sexual health on people.

What to do if you think you have chlamydia

So while koalas make for a memorable headline, human chlamydia is a completely separate infection — and one worth taking seriously, because it’s common and usually silent. If you notice any symptoms, or you think you may be at risk (a new partner, unprotected sex, or a condom that slipped or broke), it’s worth having an STI check to be sure. A positive result simply means you can get quick, effective treatment that protects your health and your partners’, and helps stop the infection spreading. Testing for chlamydia and other STIs is quick, confidential and judgement-free.