This year seems to be all about vaccination — not just for humans, but for koalas as well. However, they’re not doing it for COVID-19. 

As part of a trial, about 400 koalas will be vaccinated against chlamydia — a sexually transmitted disease (STD) also found in humans that has spread widely among the furry animals in some areas of Australia. The researchers behind the initiative hope the roll-out of the vaccine will significantly improve the survival and reproduction of the animals.

Wild koalas can get infected with chlamydia through sexual contact and newborns can contract it by eating pap, a nutritious type of feces excreted by infected mothers (yes, koalas do that). It’s not really clear why the animals are so vulnerable to the disease, with previous studies suggesting a virus in the same family as the human immunodeficiency virus (HIV) could be the reason. 

While humans are affected by the bacterium Chlamydia trachomatis, koalas are targeted by the Chlamydia pecorum — a different ‘breed’ of chlamydia, though both can cause infertility and permanent blindness if left untreated. Antibiotics used in humans can also work for koalas, but the success rate varies and some antibiotics produce harmful side effects, disrupting the koalas’ gut bacteria. 

The diet of wild koalas is based on eucalyptus leaves. While nutritious, leaves have a compound called tanning that can be highly toxic if it’s not broken down by gut bacteria — and the antibiotics seem to be causing just that, leaving koalas unable to process their meals. That’s why new antibiotics and even a vaccine have been long searched for. 

Trying out the new vaccine

The vaccine was developed by researchers at the University of the Sunshine Coast (USC) in Australia. Professor Peter Timms spent the past decade investigating the impact of chlamydia in koalas and sequencing the koala genome, which has now led to the vaccine. It has already passed Phase 1 and Phase 2 trials, with over 250 koalas vaccinated. 

Timms argues the vaccine is completely safe, with a good immune response and a decrease in the levels of chlamydia infection identified in the trials. Now, for phase 3, the plan is to vaccinate 400 animals, starting at the Australia Zoo Wildlife Hospital, the Moggill Koala Rehabilitation Center, and the RSPCA Wildlife Hospital and then continuing with animals in the wild. 

“We are now at the exciting stage of being ready to roll out the vaccine as part of large Phase 3 trials,” Timms said in a statement. “While this vaccination will directly benefit each of the animals, the trial will also have a focus on the protection provided by vaccination. All koalas will be microchipped and the hospital will record any animals that return for any reason.”

Ambert Gillett, a veterinarian at the Australia Zoo Wildlife Hospital involved in the research, said chlamydia is a “cruel disease” for koalas, causing conjunctivitis, bladder infections, and infertility. Having a vaccine will largely help to prevent infection, she added. Chlamydia is the most common reason for koala admission to the Australia Zoo Wildlife Hospital. 

As well as chlamydia, koalas are also threatened by global warming and tree-clearing. Climate change is leading to the koala range being reduced in Australia because of fewer nutritious eucalyptus leaves available. At the same time, the expansion of agriculture means koalas have to spend a longer time on the ground moving from tree to tree.