Infected Koalas Are Dying From The Antibiotics Used To Treat Them


Australia is in the midst of a chlamydia epidemic and it is koalas, not humans, who are at risk.

The strain that affects these cuddly-looking marsupials from the land down under is particularly unpleasant and can often be deadly. Unfortunately, according to a paper published in PeerJ, the medicine being used to treat the STI could be making the situation a whole lot worse.


Koala chlamydia is an extremely painful condition that is transmitted through sex or through pap, a specialized form of feces used by mothers to wean joeys. It is estimated to affect somewhere between 50 and 100 percent of the wild population.

Even in cases that don’t prove fatal, chlamydia can cause urinary tract infections, blindness, and infertility. All of which is extremely bad news for a vulnerable species that has seen numbers decline by 33 percent in just two decades.

A chlamydia vaccine is in the pipeline but for now, most cases are treated with a generous dose of antibiotics. The drugs kill the infection. The thing is, they also kill a type of gut bacteria called L. koalarum, which is crucial to the koala’s survival.

The study, led by Katherine Dahlhausen at the University of California Davis, analyzed the bacteria in 141 fecal samples from eleven koalas receiving care for chlamydia. Nine were being treated with antibiotics and two were not.

  1. L. koalarum was one of four types of “friendly gut bacteria” present before and after treatment in those that survived but was missing in one koala that died after antibiotic treatment.

  2. The bacteria is responsible for breaking down tannins, a substance found in eucalyptus leaves. Because eucalyptus leaves make up the vast majority of a koala’s diet and because tannins can be extremely harmful if not properly broken down, a shortage of L. koalarum in the gut essentially causes the koala to starve to death.

  3. So, what now?

  4. The chlamydia vaccine won’t be available for some time and there are currently no known types of antibiotics that can kill chlamydia while protecting gut bacteria. Instead, Dahlhausen told New Scientist, “fecal transplants may be the best method for offsetting the detrimental effects of antibiotics” – at least for the time being.

  5. She added, the findings are preliminary so there may be other bacteria also affected by the antibiotic treatments.

  6. The next stage is to monitor koalas over a longer timescale and work out how exactly the antibiotics affect a mother's pap. 


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