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A non-invasive tool for assessing pathogen prevalence in koala (Phascolarctos cinereus) populations: detection of Chlamydia pecorum and koala retrovirus (KoRV) DNA in genetic material sourced from scats

Wedrowicz, F, Saxton, T, Mosse, J, Wright, W & Hogan, FE 2016, Conservation Genetics Resources, vol. 8, no. 1, pp. 511-521.

The major pathogens affecting koalas, Chlamydia pecorum and koala retrovirus (KoRV), can be reliably detected in DNA isolated from faecal samples.

  The scats of koalas with a known C. pecorum or KoRV infection status, as determined by a separate study, were examined for the presence of DNA from each pathogen respectively. In five out of six koalas, the presence or absence of C. pecorum infection as detected in DNA isolated from urogenital swabs was confirmed by that from scats. One individual tested positive for C. pecorum in scat samples but not urogenital swab samples, potentially indicating infection at a site such as the gastrointestinal tract that would not necessarily return a positive result from a urogenital swab. In two out of three instances, scats and urogenital swabs exhibited identical C. pecorum ompA genotypes. The remaining instance could indicate that multiple strains were present within the same individual, possibly infecting different sites throughout the body. Previous studies have confirmed that endogenous or vertically-transmitted KoRV can be reliably detected in DNA isolated from koala scats, as all cells contain at least one KoRV copy. In the case of an exogenous KoRV infection, not all cells will be infected. In this study, KoRV copy number was significantly greater in scats from New South Wales koalas than from Victorian koalas. This finding aligns with previous reports that, unlike their New South Wales counterparts, most Victorian koalas have exogenous rather than endogenous KoRV infections. Moreover, the result suggests that the detection of these horizontally-acquired infections from scat samples is achievable, but the method may only be suitable for determining presence or absence of the virus.

  The detection of pathogens in free-ranging koala populations is not only challenging for practitioners but also stressful or invasive for the animal with sampling often involving procedures such as collection of urogenital and ocular swabs, tissue biopsies and blood extraction. Non-invasive sampling such as scat collection can, therefore, facilitate sampling at a much greater scale without any need to capture or handle the koala.

  The authors of this report describe a valuable tool for monitoring the prevalence of pathogens that have the capacity to threaten koalas across their range, with applications for conservation programs and monitoring of populations following translocations or release of individuals.

 

Summarised by Joanna Horsfall

 

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