November 6, 2019 – Koalas may be one of the world’s most unique, endearing animals, but they are increasingly vulnerable to multiple threats. Morris Animal Foundation-funded researchers at the University of Adelaide are offering hope for one problem, though - disease. The researchers recently identified what could be the last large, isolated, healthy chlamydia-free population of koalas in Australia, on Kangaroo Island.
“This is a very important finding because chlamydial disease is so prevalent and efforts to fight it have so far been unsuccessful,” said Dr. Natasha Speight, koala researcher at the University of Adelaide’s School of Animal and Veterinary Sciences. “These koalas could potentially be used as a disease-free breeding colony in the future.”
The Australian Koala Foundation (AKF) estimates that wild koalas currently number about 85,000 individuals. By comparison, the AKF reports more than 8 million koalas killed in the fur trade a century ago.
Further declines are driven by human expansion with city growth destroying habitat and fragmenting populations. Koalas are routinely hit by cars and attacked by dogs. Climate change ups the threat with increasing droughts and fires.
Diseases such as chlamydia and koala retrovirus infection pose another lethal threat. Chlamydia was first discovered in koalas in the 1970s. Caused by the bacterium Chlamydia pecorum, chlamydia is transmitted sexually or by close contact, including from mothers to joeys. When disease develops, it can cause blindness, urinary tract infection and death. Chlamydia is very common and contributes to dramatic population declines.
Koala retrovirus is in the same family of viruses as HIV and is found in every koala in northern Australia. It’s possible that koalas develop a form of koala AIDS, which compromises their ability to fight off other infectious diseases, such as chlamydia.
Dr. Speight’s team sought to determine the prevalence of C. pecorum in wild-ranging koalas. Based on previous evidence that found low or no infection rates, the team focused on koalas in the Mount Lofty Ranges (MLR), a mountain range just east of Adelaide, and Kangaroo Island (KI), Australia’s third largest island, 70 miles southwest of Adelaide.
They captured and released 75 koalas from MLR and 170 koalas from KI. Veterinarians checked each koala and collected swab samples to test for C. pecorum DNA. Researchers also examined more than 13,000 historical veterinary records of KI koalas, from over a 22-year period, for accounts of the disease.
They found that nearly half of the MLR koalas were positive for C. pecorum DNA, but the KI koalas were all C. pecorum negative and no disease was observed. There also were no definitive records of the disease in the island’s historical archives.
The team used the results in a statistical model that showed, with 95% confidence, that Kangaroo Island is C. pecorum-free. The team will next perform a risk assessment to reduce the chances of chlamydia being introduced to the island’s population.
Morris Animal Foundation is one of the only organizations funding health research for species like the koala. This latest study could be the most impactful, as the chlamydia-free population provides insurance for the future.