Prevalence and genotyping studies of koala retrovirus in Victorian koalas (Phascolarctos cinereus)

The pathogen koala retrovirus (KoRV) is present in koala populations in Victoria, Australia, but not in all individuals. This is in contrast to northern populations of koalas in Australia where KoRV is present in all... [ view full abstract ]

The pathogen koala retrovirus (KoRV) is present in koala populations in Victoria, Australia, but not in all individuals. This is in contrast to northern populations of koalas in Australia where KoRV is present in all individuals. Most KoRV studies have focused on northern koala populations in Australia, or koalas in captivity. Previous studies of KoRV in Victorian koalas have been limited to small numbers of animals. An association between KoRV and neoplasia has been reported in captive koalas, and a recent study of koalas in US zoos found a new virus genotype (KoRV-B) which was strongly associated lymphoma/leukaemia. The presence of KoRV-B in mainland Australian populations has not been described. A unique opportunity exists to use the Victorian koala population, including KoRV-negative koalas, to better understand the clinical impact of infection with KoRV, including any clinical differences between KoRV genotypes. To this end we determined the prevalence of KoRV in koalas (n = 648) across seven different regions in Victoria using a qPCR targeting the pol region of the provirus. The overall prevalence of KoRV infection was 25%, ranging from 16 – 40% across regions. We then used qPCRs targeting the env region to determine the presence of KoRV-A and KoRV-B in the koalas which tested positive (n = 160). We are now using this data, along with clinical information and our previous data relating to the presence of Chlamydia pecorum infection, to better understand the clinical significance of KoRV infection in Victorian koalas. Interestingly, our analyses have shown no significant association between Chlamydia and KoRV infection in Victorian koalas, which contradicts a long held theory. This research provides crucial information regarding prevalence and genotypes of KoRV within Victorian koala populations, which is one of the few locations where individuals of this iconic species remain free of this pathogen.