Cancer and Haematological Disease in Koalas: A Clinical and Virological Update

Jon Hanger, Jeff McKee, Rachael Tarlinton and Amanda Yates

Koalas as a species suffer from an unusually high incidence of leukaemia, lymphoma and immunosuppressive disease. These syndromes cause significant morbidity in both captive and wild koalas, and almost invariably result in death after a variable period of illness or ill-thrift.  The involvement of a gammaretrovirus in the pathogenesis of these diseases has been suspected for many years, but a solid causal link has yet to be demonstrated. Our research has shown a link between KoRV a newly discovered endogenous gammaretrovirus of koalas and this disease syndrome. Endogenous retroviruses are inherited within the host genome and are present in all members of a species. To date DNA PCR on blood samples has been positive for KoRV in every koala tested. We have developed a real time PCR for quantitation of viral RNA levels in plasma and have demonstrated that koalas with clinical leukemia or lymphoma have higher levels of viral RNA than their healthy counterparts. In addition wild koalas with clinical Chlamydia have a mean viral load higher than the mean for healthy koalas. This provides strong evidence for the association of KoRV with disease in koalas.