Australian scientists have begun vaccinating wild koalas against chlamydia in an ambitious field trial in New South Wales.
The aim is to test a method for protecting the marsupials against a widespread disease that causes blindness, infertility and death.
Samuel Phillips, a microbiologist at the University of the Sunshine Coast who helped to develop the vaccine, said: “It’s killing koalas because they become so sick they can’t climb trees to get food, or escape predators, and females can become infertile.”
The scientists’ initial goal is to catch, vaccinate and monitor around half of the koala population in the Northern Rivers region of New South Wales — that means vaccinating around 50 animals.
Now scientists want to understand the impact of vaccinating a population of wild koalas.
“We want to evaluate what percentage of the koalas we need to vaccinate to meaningfully reduce infection and disease,” said Mr Phillips.
The first koalas were caught and vaccinated in March, and the programme is expected to last about three months.
Researchers use binoculars to spot koalas in eucalyptus trees, then construct circular enclosures around the tree bases with doors leading into cages.
After a few hours or days, the koalas will eventually climb down from one tree to seek tasty leaves on another, and wander into the harmless traps.
After a check-up to make sure the animals are in good condition, researchers give them an anaesthetic and shots of vaccine, then keep them under observation for 24 hours after they wake up, to confirm there are no unexpected side-effects, she said.
The goal is to vaccinate healthy koalas to prevent them from becoming infected with chlamydia.
Before release, the researchers mark the koalas with a dab of pink dye on their backs, to ensure the same animals are not caught twice.
When the first vaccinated koala was returned to her habitat on March 9, the scientists placed her cage at the base of a tree and opened the door. She quickly emerged and bounded up the tree trunk.
Australia’s wild koala populations have declined steeply in the past two decades.
Last February, the federal government declared them “endangered” in the eastern regions of New South Wales, Queensland and the Australian Capital Territory.
Facing compounded threats from disease, habitat loss and road collisions, koalas could become extinct by 2050, according to a 2020 assessment from the New South Wales government.
Around half of wild koalas in Queensland are already infected with chlamydia, scientists estimate.
The trial was approved by multiple government bodies, including Australia’s agriculture department and New South Wales’s planning and environment department.
The origins of chlamydia in koalas have not been confirmed, but scientists believe it is likely the marsupials initially caught the disease from exposure to the faeces of infected sheep and cattle. It then spread sexually, or passed from mother to offspring.
While humans and livestock infected with the bacteria that causes chlamydia can be treated with antibiotics, it is not that simple for koalas.
The “complex” microbes inside the stomachs of koalas are designed to neutralise toxins in eucalyptus leaves that are their main food source, said Mathew Crowther, a conservation biologist at the University of Sydney. But their digestive systems can also neutralise some medicines so “that means they don’t respond well to antibiotics treatment”, he said.
Mr Crowther has been monitoring a population of koalas in northern New South Wales for more than a decade. In 2008, 10% of animals tested there were infected with chlamydia. Today that rate is 80%.
“It’s been devastating — there’s very, very low fertility,” he said. “You hardly see any babies.”
The other threats koalas face — including habitat destruction from land clearing and climate-enhanced wildfires — may increase their stress levels, weakening their immune systems and making them more susceptible to diseases including chlamydia, Mr Crowther added.
A post-mortem examination of one koala with advanced chlamydia that had been euthanised revealed “ovaries completely encased in cysts” and “intestines full of hard lumps of food, evidence that she couldn’t properly digest food”, recalled Ms Johnson. “She was obviously infertile and in pain.”
There are only a handful of other examples worldwide of scientists attempting to catch and inoculate endangered wildlife for conservation.
In 2016, scientists began to vaccinate Hawaiian monk seals against a deadly strain of morbillivirus. Two-and-a-half years ago, biologists in Brazil began to vaccinate golden lion tamarins against yellow fever.
“Vaccination for wildlife is certainly not routine yet,” said Jacob Negrey, a biologist at Wake Forest University School of Medicine. “But whether it should be used more often is a fundamental question that conservation biologists are really wrangling with right now.”
Ms Johnson said the benefits are likely to outweigh the risks for koalas. “Vaccination is an incredibly resource-intensive thing to do. Koalas live high up in trees,” she said.
“But because the effects of chlamydia are so debilitating, I think it’s totally worth it.”