18 October 2021
By Alice Klein
A vaccine designed to protect koalas against chlamydia is being tested in a large clinical trial in Queensland, Australia.
Australia’s koalas are in the grip of a chlamydia epidemic, with up to 100 per cent of some populations testing positive for the sexually transmitted infection. Its rapid spread is thought to be a major driver of plummeting koala numbers.
Peter Timms at the University of the Sunshine Coast in Queensland and his colleagues have spent more than a decade developing a vaccine to protect koalas against the disease, which can lead to painful urinary tract infections, loss of bladder control, infertility, blindness and death.
The vaccine exposes koalas to small fragments of the Chlamydia pecorum bacterium that can infect them. This trains the immune system to recognise and attack the pathogen if they become infected.
Eight small studies have shown that the vaccine protects koalas from getting sick if they catch chlamydia and can also reduce symptom severity in those that are already infected.
In the current trial, which is the biggest yet, the vaccine will be given as a single injection to 200 koalas at the Australia Zoo Wildlife Hospital in Beerwah, Queensland. The trial began on 15 October, with a koala called Shano receiving the first jab (pictured).
To evaluate the vaccine’s efficacy, Timms and his colleagues will assess how many of the 200 vaccinated koalas are hospitalised with chlamydia symptoms over the next 12 months compared with 200 unvaccinated koalas.
If the vaccine is approved for widespread use, “it could help to turn around populations of koalas that might disappear”, says Timms. His team has already found that the vaccine, combined with other veterinary care, was effective at reversing declining koala numbers in an area of south-east Queensland.
It may be possible to use similar principles to develop a vaccine for human chlamydia, which is caused by the related bacterium Chlamydia trachomatis, says Timms. “I think this trial will be closely watched by the human chlamydia vaccine world,” he says.
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