Infection with koala retrovirussubgroup B (KoRV-B), but not KoRV-A, is associated with chlamydial disease in free-ranging koalas (Phascolarctos cinereus)
Courtney A. Waugh1,2, Jonathan Hanger 3, Joanne Loader3, Andrew King4, Matthew Hobbs4, Rebecca Johnson4 & Peter Timms1
1Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs, 4558, Queensland, Australia.
2Department of Biology, Norwegian University of Science and Technology, 7491, Trondheim, Norway.
3Endeavour Veterinary Ecology, 1695 Pumicestone Rd, Toorbul, 4510, Queensland, Australia.
4Australian Museum Research Institute, Australian Museum, 1 William Street, Sydney, NSW, 2010, Australia.
Correspondence and requests for materials should be addressed to P.T. (email: )
The virulence of chlamydial infection in wild koalas is highly variable between individuals. Some koalas can be infected (PCR positive) with Chlamydia for long periods but remain asymptomatic, whereas others develop clinical disease. Chlamydia in the koala has traditionally been studied without regard to coinfection with other pathogens, although koalas are usually subject to infection with koala retrovirus (KoRV). Retroviruses can be immunosuppressive, and there is evidence of an immunosuppressive eﬀect of KoRV in vitro. Originally thought to be a single endogenous strain, a new, potentially more virulent exogenous variant (KoRV-B) was recently reported. We hypothesized that KoRV-B might signifcantly alter chlamydial disease outcomes in koalas, presumably via immunosuppression. By studying subgroups of Chlamydia and KoRV infected koalas in the wild, we found that neither total KoRV load (either viraemia or proviral copies per genome), nor chlamydial infection level or strain type, was signifcantly associated with chlamydial disease risk. However, PCR positivity with KoRV-B was signifcantly associated with chlamydial disease in koalas (p= 0.02961). This represents an example of a recently evolved virus variant that may be predisposing its host (the koala) to overt clinical disease when coinfected with an otherwise asymptomatic bacterial pathogen (Chlamydia).