Prevalence of koala retrovirus in geographically diverse populations in A ustralia

Objective To determine the prevalence of koala retrovirus ( KoRV ) in selected koala populations and to estimate proviral copy number in a subset of koalas. Methods Blood or tissue samples from 708 koalas in Q ueensland, N ew S outh W ales, V ictoria and S outh A ustralia were tested for KoRV pol provirus gene using standard polymerase chain reaction ( PCR ), nested PCR and real‐time PCR ( qPCR ). Results Prevalence of KoRV provirus‐positive koalas was 100% in four regions of Q ueensland and N ew S outh W ales, 72.2% in mainland V ictoria, 26.6% on four V ictorian islands and 14.8% on K angaroo I sland, S outh A ustralia. Estimated proviral copy number per cell in four groups of koalas from Q ueensland and V ictoria showed marked variation, ranging from a mean of 165 copies per cell in the Q ueensland group to 1.29 × 10 −4 copies per cell in one group of V ictorian koalas. Conclusions The higher prevalence of KoRV ‐positive koalas in the north of A ustralia and high proviral loads in Q ueensland koalas may indicate KoRV entered and became endogenous in the north and is spreading southwards. It is also possible there are genetic differences between koalas in northern and southern Australia that affect susceptibility to KoRV infection or endogenisation, or that environmental factors affecting transmission in northern states are absent or uncommon in southern regions. Although further studies are required, the finding of proviral copy numbers orders of magnitude lower than what would be expected for the presence of a single copy in every cell for many V ictorian animals suggests that KoRV is not endogenous in these animals and likely reflects ongoing exogenous infection.