Epidemiology of chlamydial infection and disease in a free-ranging koala (Phascolarctos cinereus) population

Abstract

Chlamydial disease continues to be one of the main factors threatening the long-term survival of the koala (Phascolarctos cinereus). Despite this, large epidemiological studies of chlamydial infection and disease in wild koala populations are lacking. A better understanding of the prevalence, transmission and pathogenesis is needed to improve control measures, such as the development of vaccines. We investigated the prevalence of Chlamydia pecorum infection and disease in 160 koalas in a peri-urban wild population in Queensland, Australia and found that 31% of koalas were Chlamydia PCR positive and 28% had clinically detectable chlamydial disease. Most infections were at the urogenital site (27%; both males and females) with only 14% at the ocular site. Interestingly, we found that 27% (4/15) of koalas considered to be sexually immature (9–13 months) were already infected with C. pecorum, suggesting that a significant percentage of animals are infected directly from their mother. Ocular infection levels were less prevalent with increasing age (8% in koalas older than 4 years), whereas the prevalence of urogenital tract infections remained high into older age (26% in koalas older than 4 years), suggesting that, after mother-to-young transmission, C. pecorum is predominantly a sexually transmitted infection. While 28% of koalas in this population had clinically detectable chlamydial disease (primarily urogenital tract disease), many PCR positive koalas had no detectable disease and importantly, not all diseased animals were PCR positive. We also observed higher chlamydial loads in koalas who were C. pecorum infected without clinical disease than in koalas who were C. pecorum infected with clinical disease. These results shed light on the potential mechanisms of transmission of C. pecorum in koalas and also guide future control measures, such as vaccination.

Using non-invasive sampling methods to determine the prevalence and distribution of Chlamydia pecorum and koala retrovirus in a remnant koala population with conservation importance

“…This is important because the high costs associated with traditional sampling make the study of pathogens in wild populations rare in the literature (e.g. Nyari et al 2017;Quigley et al 2018). This study also represents the first large-scale investigation of the prevalence and spatial 40 distribution of C. pecorum and KoRV-A in the wild South Gippsland koala population, and was made possible by use of non-invasive DNA sampling from koala scats.…”

“…Cape Otway and Mallacoota in Victoria), where the prevalence of C. pecorum is very low (Emmin 1996; Legione et al 2016a, 20 2016b), this does not appear to be due to a lower prevalence of infection. A recent study of 160 koalas in south-east Queensland found a C. pecorum infection rate of 31% (Nyari et al 2017). This study shows that the prevalence of C. pecorum infection in some Victorian koala populations 25 (South Gippsland and Raymond Island) is not lower than that in northern koala populations.…”

“…Knowledge of the different pathogen genotypes present in a population may be important when considering management actions such as animal translocation. Virulence of C. pecorum strains infecting koalas and other animal hosts may vary 40 (Mohamad et al 2014;Nyari et al 2017), and the severity of disease may differ depending on the health of the individual animal or the presence of environmental stressors that may impact health and therefore disease susceptibility (Timms 2005;Lunney et al 2012;McAlpine et al 2017). The 45 potential for exposure to new chlamydial strains that may have negative health impacts is an important consideration for proposed translocations.…”

“…Two pathogens, Chlamydia pecorum and koala retrovirus (KoRV), infect koalas and are often cited as major contributors to population decline (EaCRC 2011a), despite a limited 30 understanding of their role in host population dynamics (Grogan et al 2017;McCallum et al 2017). Large-scale population level studies of koala pathogens are lacking in the literature (but see Nyari et al 2017;Quigley et al 2018). This may be due, in part, to the challenges associated with koala 35 capture, which can be stressful to koalas, potentially resulting in death (Radford et al 2006;Phillips 2011).…”

Chlamydiae from Down Under: The Curious Cases of Chlamydial Infections in Australia

“…Koala Cpec infections and the resultant debilitating disease deserve rather constant updates to aid in an ongoing tireless effort in the control of these infections and successful management of the infected koalas. Cpec infects almost all of Australia's mainland koala populations spanning from northern (Qld and NSW) to the southern states (Vic and South Australia (SA)) [98][99][100][101][102]. However, a recent study estimating Cpec prevalence in SA koala populations, showed that the geographically separated Kangaroo Island koala population was infection-and disease-free, whereas the mainland population was not [103].…”