First wild koalas caught and vaccinated against chlamydia
By CHRISTINA LARSON
Australian scientists have begun vaccinating wild koalas against chlamydia in an ambitious field trial in New South Wales.
The goal is to test a method to protect the beloved marsupials from a widespread disease that causes blindness, infertility and death.
“It kills koalas because they get so sick they can’t climb trees to get food or escape predators, and females can become sterile,” said Samuel Phillips, a microbiologist at the University of the Sunshine Coast who helped with the development of the vaccine.
The scientists’ original goal is to capture, vaccinate and monitor about half of the koala population in the Northern Rivers region of New South Wales – that means vaccinating about 50 animals.
The safety and effectiveness of the single vaccine, which was designed specifically for koalas has previously been tested by vaccinating a few hundred koalas brought to wildlife sanctuaries for other conditions.
Now scientists want to understand the impact of vaccinating a population of wild koalas. “We want to evaluate what percentage of koalas we should vaccinate to meaningfully reduce infection and disease,” Phillips said.
The first koalas were captured and vaccinated in March, and the effort is expected to last about three months.
Researchers use binoculars to spot koalas in eucalyptus trees, then build circular enclosures around the tree bases with doors leading to cages. After a few hours or days, the koalas will eventually climb down from one tree to find tasty leaves from another tree and end up in the harmless traps.
“It’s hard to confuse a koala with other animals — they’re pretty easy to spot,” says Jodie Wakeman, veterinary care and clinical director at Friends of the Koala, a nonprofit organization that runs an animal hospital where the koalas go. are being brought. vaccination.
After checking to make sure the animals are in good condition, the researchers administer anesthesia and injections of the vaccine, then observe them for 24 hours after awakening to confirm there are no unexpected side effects, Wakeman said.
The aim is to vaccinate healthy koalas to prevent them from becoming infected with chlamydia.
Before releasing them, the researchers mark the koalas with a bit of pink dye on their backs to make sure the same animals aren’t 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 emerged quickly and jumped up the tree trunk.
Koalas are iconic Australian marsupials, like wombats and kangaroos. They spend most of their time feeding and sleeping in eucalyptus trees, and their legs have two opposing thumbs to help them grab and climb up trunks.
Australia’s wild koala populations have declined sharply over the past two decades.
Last February, Australia’s federal government declared koalas “endangered” in the eastern regions of New South Wales, Queensland and the Australian Capital Territory.
According to a 2020 assessment, koalas could be extinct by 2050 if they face an even greater threat from disease, habitat loss and traffic accidents from the Government of New South Wales.
About half of Queensland’s wild koalas are already infected with chlamydia, scientists estimate.
When deciding whether to vaccinate, the scientists weigh the risk of disturbing the animals and the risk of the disease spreading. The trial was approved by multiple government agencies, including the Australian Department of Agriculture and the New South Wales Planning and Environment Department.
The origin of chlamydia in koalas is unconfirmed, but scientists think it’s likely that the marsupials initially contracted the disease from exposure to the faeces of infected sheep and cattle. Then it is spread sexually, or passed from mother to offspring.
While people and livestock infected with the bacteria that causes chlamydia can be treated with antibiotics, it’s not so easy for koalas.
The “complex” microbes in koalas’ stomachs are designed to neutralize toxins in eucalyptus leaves, which are their main food source, says Mathew Crowther, a conservation biologist at the University of Sydney. But their digestive systems can also neutralize some drugs, “that means they don’t respond well to antibiotics,” he said.
Crowther has been tracking a population of koalas in northern New South Wales for more than a decade. In 2008, 10% of the animals tested there were infected with chlamydia. Today that percentage is 80%.
“It’s been devastating — there’s very, very low fertility,” he said. “You hardly see any babies.”
The other threats facing koalas, including habitat destruction from land clearing and climate-induced wildfires — can increase their stress levels, weaken their immune systems and make them more susceptible to diseases like chlamydia, Crowther said.
Rebecca Johnson, now chief scientist at the Smithsonian National Museum of Natural History in Washington, DC, previously led Australia’s Koala Genome Consortium. She said it was heartbreaking to see the effects of the disease up close.
An autopsy of a koala with advanced chlamydia who was euthanized revealed “ovaries completely enclosed in cysts” and “guts packed with hard clumps of food, evidence that she couldn’t digest food properly,” Johnson recalled. “She was clearly infertile and in pain.”
There are only a handful of other examples worldwide of scientists attempting to capture and vaccinate endangered wildlife for conservation purposes. In 2016, scientists began vaccinating Hawaiian monk seals against a deadly strain of morbillivirus. Two and a half years ago, biologists in Brazil started vaccinating golden lion tamarins against yellow fever.
“Wildlife vaccination 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 grappling with right now.”
Johnson of the Smithsonian said the benefits likely outweigh the risks to koalas. “Vaccination is an incredibly labor intensive thing to do. Koalas live high in trees,” she said.
“But because the effects of chlamydia are so debilitating, I think it’s totally worth it.”
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Follow Christina Larson on Twitter: @larsonchristina
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