Two infectious pathogens contributing to northern Australian (Queensland and New South Wales) population declines are Chlamydia pecorum and koala retrovirus (KoRV). C. pecorum infection causes conjunctivitis and blindness, urinary tract infections or reproductive tract disease causing infertility. In northern populations, KoRV-A is 100% prevalent and an active endogenous virus. High KoRV viral load and exogenous KoRV-B have been associated with lymphosarcoma and chlamydial disease. In South Australia (SA), less is known about C. pecorum and KoRV prevalence and disease, though early evidence has suggested that chlamydial disease is less severe and KoRV prevalence is low. SA koalas may therefore provide an opportunity to further investigate the association of KoRV with disease. The prevalence of C. pecorum and KoRV was determined in wild-caught SA koalas. The Kangaroo Island (KI) population was shown to be C. pecorum-free by qPCR (n=170) and in historical clinical data (n=13,000). In the Mount Lofty Ranges (MLR), 46.7% (35/75) of koalas were C. pecorum positive, and whilst only 4.0% (3/75) were observed with disease, C. pecorum infection was significantly associated with female reproductive inactivity. The prevalence of KoRV in KI and MLR was 42.4% (72/170) and 65.3% (49/75), respectively and only KoRV-A and not KoRV-B was detected by PCR. The median (range) KoRV proviral load in KI and MLR was low, at 113 (2- 12,641) and 35 (1- 574) copies/103 β-actin copies, respectively. There was no association between C. pecorum infection or disease and KoRV provirus, however koalas with concurrent infections were over three times more likely to develop chlamydial disease. Subclinical C. pecorum and KoRV infections were shown to have no effect on haematology values, allowing for the development of the first southern koala haematology reference intervals (n=138). An extensive comparative pathological investigation was conducted on KoRV-positive koalas from the MLR (n=92) and Queensland (n=67). Lymphosarcoma was observed in 4.3% (4/92) of MLR and 7.5% (5/67) of Queensland koalas, with the same morphology and high KoRV proviral and viral loads, that may suggest common oncogenic pathways. Ocular chlamydial disease was severe in both populations, but urinary tract disease was less severe in MLR. There was no association between chlamydial disease severity or load and KoRV proviral load, but in MLR there was a positive correlation between chlamydial disease severity and KoRV viral load. In both populations, KoRV proviral and viral loads were positively correlated with lymphocyte and metarubricyte counts and negatively correlated with erythrocyte and neutrophil counts which may suggest that KoRV can infect bone marrow and disrupting cellular differentiation. KoRV viral load was positively correlated with splenic lymphoid area suggesting that spleen may also be a site for KoRV replication. The prevalence of C. pecorum and KoRV in mainland SA was higher than expected and severe chlamydial disease and lymphoid neoplasia do occur. No clear association between C. pecorum disease and KoRV were identified, however KoRV infection appears to be highly complex and differs between northern and southern populations. Southern populations with a reduced prevalence of disease may therefore ensure the longevity of the species.Thesis (Ph.D.) -- University of Adelaide, School of Animal and Veterinary Sciences, 201
