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

Abstract

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.

Chlamydia Psittaci ST24: Clonal Strains of One Health Importance Dominate in Australian Horse, Bird and Human Infections

“…The detection of C. psittaci in a wallaby joint in this study is the first detection of C. psittaci in a marsupial. However, the severe impact of C. pecorum infections on Australian koalas, resulting in reproductive, urinary, and ocular disease, is well known [ 8 , 29 ]. Earlier reports of C. psittaci in koalas have since been revised, and to date, there remains no evidence of C. psittaci in koalas, nor any other marsupial.…”

Koala Retrovirus in Northern Australia Shows a Mixture of Stable Endogenization and Exogenous Lineage Diversification within Fragmented Koala Populations

“…Previous study has determined that KoRV proviral profiles generated from multiple sample types can be combined for analysis (12), so all samples were DNA extracted, PCR amplified to obtain the KoRV envelope gene receptor binding region from all subtypes simultaneously, deep amplicon sequenced and processed to obtain representative operational taxonomic units (OTUs) or strains present in each koala. This procedure is on February 1, 2021 by guest http://jvi.asm.org/ Downloaded from analogous to several previous KoRV proviral studies (7,11,12,19,20). Study samples generated an average of 188,016 ± 69,301 KoRV proviral reads, with an overall average Good's coverage estimate of 0.999996, meaning that overall, each sample was predicted to have been profiled to 99.9996% completion.…”

The Koala Immune Response to Chlamydial Infection and Vaccine Development—Advancing Our Immunological Understanding

“…Studies investigating the allelic diversity of class II subunits within DA and DB genes have found that the beta subfamilies (DAB and DBB) contain more allelic diversity than the alpha subfamilies (DAA and DAA), leading to more focus on the beta subfamilies in research studies [ 45 ]. As such, the current collection of sequenced koala MHC class II alleles stands at three DAA, 42 DAB, three DBA, 26 DBB, three DCB, and four DMB alleles, with DCA and DMA alleles yet to be characterised [ 43 , 47 , 48 ].…”

“…In the same population, koalas possessing the DBB*04 allele had higher levels of Chlamydia heat shock protein 60 (c-hsp60) antibody levels than koalas without DBB*04 [ 47 ]. Moving further north to examine koalas already infected with Chlamydia in southeast Queensland, Australia, DAB*10 and DBB*04 alleles again emerged with significant associations, but to different circumstances [ 48 ]. In these infected koalas, both DAB*10 and UC*01:01 alleles were significantly more prevalent in infected koalas that did not progress to clinical disease, while DBB*04 and DCB*03 alleles were significantly more prevalent in infected koalas that did progress to clinical disease [ 48 ].…”

“…Moving further north to examine koalas already infected with Chlamydia in southeast Queensland, Australia, DAB*10 and DBB*04 alleles again emerged with significant associations, but to different circumstances [ 48 ]. In these infected koalas, both DAB*10 and UC*01:01 alleles were significantly more prevalent in infected koalas that did not progress to clinical disease, while DBB*04 and DCB*03 alleles were significantly more prevalent in infected koalas that did progress to clinical disease [ 48 ]. Finally, a modelling study that also looked at southeast Queensland koalas found that knowing the MHC class II DAB and DBB profiles of a koala improved the likelihood of predicting a koala’s chlamydial disease status and that koalas without DBB*03 were more likely to have clinical chlamydial disease [ 49 ].…”