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Infection & disease

Prevalence and pathologic features of Chlamydia pecorum infections in South Australian koalas (Phascolarctos cinereus)

Speight, KN, Polkinghorne, A, Penn, R, Boardman, W, Timms, P, Fraser, T, Johnson, K, Faull, R, Bate, S & Woolford, L 2016, Journal of Wildlife Diseases, vol. 52, no. 2, pp. 301-306.

Previously thought to be of low prevalence in South Australian populations, chlamydial infection has been detected in a significant proportion of a subset of koalas from the region. For these koalas, however, infection does not necessarily lead to clinical disease.

  Post-mortem analyses were conducted for 65 koalas from the Mount Lofty Ranges and Eyre Peninsula in South Australia that were deceased or euthanised for humane reasons. Ocular and urogenital swabs were collected from each animal and tested for Chlamydia pecorum using the polymerase chain reaction (PCR) technique. Out of 65 koalas, 57 (88%) tested positive for C. pecorum; 50 in ocular swabs, 40 in urogenital swabs, and 34 in both ocular and urogenital swabs. Chlamydial lesions were found in 41 out of 57 koalas infected with C. pecorum. Of these 41 koalas, 12 expressed symptoms of overt clinical disease including conjunctivitis and staining around the cloaca, or ‘wet bottom/dirty tail’. The remaining 29 koalas had no externally apparent overt disease but had lesions that were either limited to the urogenital tract or only microscopically detectable. These lesions were typically mild and included conjunctivitis, cystitis and urethritis. Unlike the situation in Australia’s eastern states, reproductive tract disease was uncommon in these South Australian koalas. Sixteen koalas were subclinical carriers of the infection, testing positively for C. pecorum but demonstrating no symptoms of disease. Fourteen of these subclinical carriers were males.

  The prevalence of C. pecorum infection in South Australian koala populations is poorly understood compared to that in Queensland and New South Wales where the infection is ubiquitous and, consequently, highly studied. Rates of chlamydial infection in South Australian koalas are suggested here to be much higher than previously assumed. Perhaps the pathogen is less visible in southern populations because infection does not appear to lead to disease as frequently as in eastern populations. Regardless, the potentially high prevalence of C. pecorum in South Australian koalas as indicated in this report highlights the threat the pathogen may pose to populations in the region. In particular, the possibility that male koalas are more likely to be subclinical carriers of chlamydial infection than females suggests that these individuals may be a cryptic yet significant transmitter of the pathogen to naïve koalas and warrants further investigation.

 

Summarised by Joanna Horsfall

 

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