title: Infection with koala retrovirus subgroup B (KoRV-B), but not KoRV-A, is associated with chlamydial disease in free-ranging koalas (Phascolarctos cinereus).
abstract: 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 significantly alter chlamydial disease outcomes in koalas, presumably via immunosuppression. By studying sub-groups 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 significantly associated with chlamydial disease risk. However, PCR positivity with KoRV-B was significantly 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 co-infected with an otherwise asymptomatic bacterial pathogen (Chlamydia).
authors.affiliation: Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs, 4558, Queensland, Australia.|Department of Biology, Norwegian University of Science and Technology, 7491, Trondheim, Norway.
authors.forename: Courtney A
authors.initials: CA
authors.lastname: Waugh
authors.affiliation: Endeavour Veterinary Ecology, 1695 Pumicestone Rd, Toorbul, 4510, Queensland, Australia.
authors.forename: Jonathan
authors.identifier: 0000-0002-6489-4600
authors.initials: J
authors.lastname: Hanger
authors.affiliation: Endeavour Veterinary Ecology, 1695 Pumicestone Rd, Toorbul, 4510, Queensland, Australia.
authors.forename: Joanne
authors.initials: J
authors.lastname: Loader
authors.affiliation: Australian Museum Research Institute, Australian Museum, 1 William Street, Sydney, NSW, 2010, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: King
authors.affiliation: Australian Museum Research Institute, Australian Museum, 1 William Street, Sydney, NSW, 2010, Australia.
authors.forename: Matthew
authors.initials: M
authors.lastname: Hobbs
authors.affiliation: Australian Museum Research Institute, Australian Museum, 1 William Street, Sydney, NSW, 2010, Australia.
authors.forename: Rebecca
authors.identifier: 0000-0003-3035-2827
authors.initials: R
authors.lastname: Johnson
authors.affiliation: Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs, 4558, Queensland, Australia. ptimms@usc.edu.au.
authors.forename: Peter
authors.initials: P
authors.lastname: Timms
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000821:virology; D002690:Chlamydia Infections / Q000821:virology*; D005260:Female; D008297:Male; D048368:Phascolarctidae / Q000235:genetics / Q000821:virology*; D012190:Retroviridae / Q000472:pathogenicity; D012192:Retroviridae Infections / Q000821:virology*; D012307:Risk Factors