Document ID: chunk:federal_register_of_legislation:F2022L00555:body:0:p57
Version: federal_register_of_legislation:F2022L00555
Segment Type: other
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Character Range: 181833–184820

and throughout the 1920s and 1930s, and was thought to be a component of the Koala's natural history (Phillips 1990), although recent genomic comparisons suggest that some Koala C. pecorum strains may originate from domestic livestock (Bachmann et al. 2014). This is an important question to resolve as, if like KoRV (see below) C. pecorum is an evolutionarily recent introduction, its likelihood for impact on populations is likely to significant.
Koala undergoing a health check. Image: © Michael Weinhardt.
Multiple year studies and regional comparisons indicate that Chlamydia infection rates and disease severity of disease vary with time and population (range: 4% to 71%) (Quigley and Timms 2020), most likely influenced by a range of pathogen, host and environmental pressures including chlamydial strain (Fernandez et al. 2019; Robbins et al. 2020), aspects of coinfection with KoRV and other pathogens (Waugh et al. 2017; Quigley et al. 2018; Quigley et al. 2019; Robbins et al. 2020), host genetics such as MHC type (Cheng et al. 2018; Jobbins et al. 2012; Lau et al. 2014; Johnson et al. 2018; Robbins et al. 2020) and likely other environmental factors such as habitat and climatic stressors (Narayan and Williams 2016), and behavioural/ transmission dynamics. Chronic stress to individual Koalas from poor nutrition, reduced habitat quality (habitat loss, fragmentation, degradation and drought), exposure to unnatural situations (predation, dogs and traffic), heat-stress, bushfires or other factors, is likely to lead to the production of glucocorticoids (stress hormones), which can inhibit reproductive hormones and immune responses, reducing individual health (McAlpine et al. 2017; Narayan and Williams 2016). Where these factors become widespread and chronic, such as in areas of urban and peri-urban landscapes or in areas of marginal habitat quality (Davies et al. 2013), it is possible that loss of fertility due to disease and reduced recruitment due to habitat fragmentation will cause populations to decline and may inhibit recovery efforts.
KoRV is a gamma retrovirus that has been found to have integrated into the Koala germ line (endogenization – facilitating transmission from parent to offspring) of northern Koala populations (100% prevalence in Queensland and New South Wales), while it is believed to be exogenous (transmitted between Koalas through infection) in the southern populations (variable presence in Victoria and South Australia) (Ishida et al. 2015). There are also several other endogenous, exogenous functional and defective subtypes and retroviral elements involved to varying degrees within and between northern and southern populations. KoRV insertion sites have recently been shown to cause cancers such as lymphosarcoma, which are common in Koalas (McEwen et al. 2021) and it is likely that deleterious insertions interfere with a range of immune and metabolic genes, though evidence for this is preliminary. Given its evolutionarily