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Koalas face dual threat of disease and inbreeding
A team of researchers in South Australia is attempting an unprecedented genetic rescue mission to save Kangaroo Island's koalas, the world's largest chlamydia-free population. The effort comes as the species faces a perfect storm of habitat loss, disease, and shrinking genetic diversity.
Chlamydia epidemic ravages mainland populations
Up to 88% of koalas in some mainland regions are infected with Chlamydia pecorum, a bacterium that causes blindness, infertility, and often fatal pneumonia. Unlike human chlamydia, the strain affecting koalas is frequently deadly. Conservation biologist Karen Burke Da Silva, from Flinders University, recently captured a female koala in Belair National Park near Adelaide, where she suspects the animal is infected.
While antibiotics can treat the disease, the process is complex. Koalas must be sedated, and the drugs can disrupt their ability to digest eucalyptus leaves, their primary food source. A vaccine approved in 2025 has reduced mortality by 65% in wild populations, but scaling up vaccination remains a challenge.
Kangaroo Island: A refuge with its own crisis
Kangaroo Island, located 13 km (8 miles) off Australia's southern coast, hosts the largest chlamydia-free koala population in the world. However, the island's koalas are descended from just 20 individuals introduced in the 1920s to prevent extinction from the fur trade. By 2019, their numbers had swelled to 50,000, but the 2019-20 Black Summer bushfires killed 80% of the population, leaving around 10,000 survivors.
Natasha Speight, a koala researcher at the University of Adelaide, confirms the island's population remains free of chlamydia, making it a critical genetic reservoir. Yet, more than a century of isolation has left the koalas deeply inbred, with visible deformities such as missing testicles and spinal abnormalities.
Genetic rescue: A first for koalas at this scale
Burke Da Silva and her colleague Julian Beaman are leading an ambitious project to restore genetic diversity to Kangaroo Island's koalas. Their plan involves introducing genetically diverse, chlamydia-free males from the mainland to breed with local females. The team has already secured a 530-hectare (1,300-acre) sanctuary bordering Flinders Chase National Park, home to roughly 1,000 koalas-about 10% of the island's remaining population.
"This is the first time genetic rescue will have been done for koalas at this scale," says Carolyn Hogg, chair of the Australasian Wildlife Genomics Group at Sydney University. The project aims to create a population that is both genetically robust and disease-free, serving as a model for other fragmented wildlife populations.
How the rescue will work
The team will fence off sections of forest where mainland males and island females can breed naturally. Radio collars and automated gates will eventually allow only genetically diverse offspring to enter Flinders Chase National Park. The first translocation is planned for late 2026, with males sourced from a high-diversity colony near the South Australia-Victoria border.
To minimize risks, the researchers are testing genetic compatibility by pairing mainland males with Kangaroo Island females at Cleland Wildlife Park. They are also developing computer simulations to model breeding outcomes based on population size, sex ratios, and age structure.
From sanctuary to mainland reintroduction
Once genetic diversity is restored, the team plans to reintroduce the koalas to mainland areas with low chlamydia rates. The New South Wales government has already expressed interest in using these koalas for future reintroductions. However, exposing the animals to chlamydia could undo years of conservation work.
"What we're doing here is testing how to manage genetically fragile populations before it's too late," Beaman says. "Koalas are fragmented, isolated, and vulnerable. If we don't act now, we risk losing them to a death by a thousand cuts."
Balancing science and cultural heritage
The Koala Sanctuary, set to open to tourists in spring 2026, will fund ongoing research and conservation efforts. Burke Da Silva and Beaman are also collaborating with the Ngarrindjeri community and other Aboriginal groups to share access to the land for cultural ceremonies.
"Ultimately, it's not just on us to heal nature. We need to rediscover what it means for us to be healed by nature as well."
Karen Burke Da Silva, Conservation Biologist
Looking ahead
By 2027, the team hopes to begin repopulating Flinders Chase National Park and parts of mainland Australia with genetically resilient, disease-free koalas. The project could serve as a blueprint for managing other wildlife populations before they reach a crisis point.
Despite the challenges, Hogg remains optimistic. "This is more than achievable with careful planning," she says. "Preserving Kangaroo Island's koalas will complement broader efforts to protect the species, including habitat restoration, vaccination programs, and genetic rescue of other vulnerable populations."
