Chlamydia pecorum Infection in the Male Reproductive System of Koalas ( Phascolarctos cinereus )

Chlamydial disease threatens many of Australia’s koala populations, and yet our understanding of chlamydial epidemiology and disease dynamics in koalas is limited by a lack of comprehensive, longitudinal population studies. To address this, we utilised longitudinal samples from a large-scale population study of wild koalas in south-east Queensland, to follow chlamydial infections over time and to investigate some of the drivers of disease progression. Our findings show, firstly, that almost two thirds of chlamydial infections progressed to disease, challenging the notion that chlamydial infections in koalas commonly remain chronic and asymptomatic. Secondly, disease progression at the urogenital tract site was associated with infection load, and urogenital tract shedding was significantly higher when koalas acquired a new infection. Thirdly, chronic chlamydial exposure was not necessary for pathogenic sequelae to develop, such as infertility and mortality. Fourthly, ompA-characterised strain sub-types may reflect tissue tropisms and pathogenicity, and the chlamydial status of some chronically infected koalas may be explained by reinfections with novel genotypes. Finally, successful antimicrobial treatment provided only short-term protection against reinfection and disease progression in susceptible koalas. These findings highlight the importance of identifying and preventing chlamydial infections in koalas, informing new population management strategies and research priorities.

Section: Discussionmentioning

confidence: 90%

Longitudinal study of wild koalas (Phascolarctos cinereus) reveals chlamydial disease progression in two thirds of infected animals

Robbins

Hanger

Jelocnik

et al. 2019

“…For example, koalas with substantial chronic Chlamydia -associated structural pathology may be PCR-negative and lack chlamydial inclusion bodies, and conversely higher loads can be observed in infected asymptomatic animals then those with clinical disease 40–42 . A recent study on Chlamydia pecorum in the male koala reproductive system demonstrated 70% of morphologically normal samples and 89% of abnormal samples were qPCR positive 43 . Typically studies utilizing active surveillance document elevated frequencies of milder chlamydial infections, compared with this study emphasizing bias in sampling methodology 44 .…”

Section: Discussionmentioning

confidence: 97%

A Necropsy Study of Disease and Comorbidity Trends in Morbidity and Mortality in the Koala (Phascolarctos cinereus) in South-East Queensland, Australia

González-Astudillo

Henning

Valenza

et al. 2019

Koalas are an iconic Australian marsupial undergoing precipitous population reduction in South-East Queensland from complex interacting threats. To investigate the causes of death and the interaction of comorbidities with demography in South-East Queensland koalas, a large scale, high-throughput prospective necropsy survey was conducted spanning 2013–2016. During this period, 519 necropsies were conducted in 155 young/subadult koalas, 235 mature, 119 old koalas and 10 of unknown age. Similar numbers of males and females were assessed. Trauma and infectious disease at were the most common single diagnoses. However, comorbidity was frequent, including multicentric infection or infectious disease in combination with trauma or senescence. Female koalas had proportionally more reproductive chlamydiosis compared to males in which the ocular and urinary systems were more commonly affected. Comorbidity and disease were strongly associated with poor body condition, and trauma was associated with good body condition. Animals affected by motor vehicle trauma were often in better body condition than those affected by animal attack, tree fall or other causes of trauma. This study identified a higher frequency of infections and comorbidity then previously reported, confirming the complex nature of interacting threats to the koala population.

“…In south east Queensland (SE Qld), a population prevalence for chlamydial infection and disease of up to 73% and 53%, respectively, has been reported 3 , 4 . Chlamydial infections predominantly cause inflammatory and fibrotic disease in the eyes and urogenital tract of susceptible koalas 5 – 7 , and can result in blindness, infertility and death 2 . Consequently, population management programs that incorporate chlamydial disease control, as well as manage concurrent threats, can reverse the extinction trajectory of these declining populations 1 , 8 .…”

Section: Introductionmentioning

confidence: 99%

Koala immunogenetics and chlamydial strain type are more directly involved in chlamydial disease progression in koalas from two south east Queensland koala populations than koala retrovirus subtypes

Robbins

Hanger

Jelocnik

et al. 2020

Chlamydial disease control is increasingly utilised as a management tool to stabilise declining koala populations, and yet we have a limited understanding of the factors that contribute to disease progression. To examine the impact of host and pathogen genetics, we selected two geographically separated south east Queensland koala populations, differentially affected by chlamydial disease, and analysed koala major histocompatibility complex (MHC) genes, circulating strains of Chlamydia pecorum and koala retrovirus (KoRV) subtypes in longitudinally sampled, well-defined clinical groups. We found that koala immunogenetics and chlamydial genotypes differed between the populations. Disease progression was associated with specific MHC alleles, and we identified two putative susceptibility (DCb 03, DBb 04) and protective (DAb 10, UC 01:01) variants. Chlamydial genotypes belonging to both Multi-Locus Sequence Typing sequence type (ST) 69 and ompA genotype F were associated with disease progression, whereas ST 281 was associated with the absence of disease. We also detected different ompA genotypes, but not different STs, when long-term infections were monitored over time. By comparison, KoRV profiles were not significantly associated with disease progression. These findings suggest that chlamydial genotypes vary in pathogenicity and that koala immunogenetics and chlamydial strains are more directly involved in disease progression than KoRV subtypes.