Koala retrovirus (KoRV) genotyping analyses reveal a low prevalence of KoRV-A in Victorian koalas and an association with clinical disease.

Koala retrovirus (KoRV) is currently undergoing endogenisation into the genome of koalas in Australia, providing an opportunity to assess the effect of retrovirus infection on the health of a population. The prevalence of KoRV in north eastern Australia (Queensland and New South Wales) is 100%, whereas previous preliminary investigations in south eastern Australia (Victoria) suggested KoRV is present at a lower prevalence, although the values have varied widely. Here we describe a large study of free ranging koalas in Victoria to estimate the prevalence of KoRV and assess the clinical significance of KoRV infection in wild koalas. Blood or spleen samples from 648 koalas where tested for KoRV provirus using PCRs to detect pol and env genes. The prevalence of KoRV in these Victorian koalas was 24.7% (160/648) (95% confidence interval [CI]: 21.3, 28.1%). KoRV-A was detected in 141/160 cases but KoRV-B, a genotype associated with neoplasia in captive koalas, was not detected. Detection may have been precluded by genomic differences between KoRV in Victoria and type strains. Factors associated with KoRV infection, based on multivariable analysis, were low body condition score, region sampled, and 'wet bottom'(a staining of the fur around the rump associated with chronic urinary incontinence). Koalas with wet bottom were nearly twice as likely to have KoRV provirus detected than those without wet bottom (odds ratio = 1.90, 95% CI 1.21, 2.98). Our findings have important implications for the conservation of this iconic species, particularly in regards to translocation potential.