Genetic markers of Chlamydia pecorum virulence in ruminants support short term host-pathogen evolutionary relationships in the koala, Phascolarctos cinereus

Cristina M Fernandez; Mark B Krockenberger; Mathew S Crowther; Valentina S A Mella; Lachlan Wilmott; Damien P Higgins

doi:10.1016/j.meegid.2023.105527

Genetic markers of Chlamydia pecorum virulence in ruminants support short term host-pathogen evolutionary relationships in the koala, Phascolarctos cinereus

Infect Genet Evol. 2023 Dec:116:105527. doi: 10.1016/j.meegid.2023.105527. Epub 2023 Nov 15.

Authors

Cristina M Fernandez¹, Mark B Krockenberger², Mathew S Crowther³, Valentina S A Mella⁴, Lachlan Wilmott⁵, Damien P Higgins⁶

Affiliations

¹ Faculty of Science, Sydney School of Veterinary Science, The University of Sydney, Camperdown, Sydney 2006, NSW, Australia.
² Faculty of Science, Sydney School of Veterinary Science, The University of Sydney, Camperdown, Sydney 2006, NSW, Australia; Sydney Infectious diseases, The University of Sydney, Camperdown, Sydney 2006, NSW, Australia.
³ Faculty of Science, School of Life and Environmental Science, The University of Sydney, Sydney 2006, New South Wales, Australia.
⁴ Faculty of Science, Sydney School of Veterinary Science, The University of Sydney, Camperdown, Sydney 2006, NSW, Australia; Faculty of Science, School of Life and Environmental Science, The University of Sydney, Sydney 2006, New South Wales, Australia.
⁵ NSW Department of Planning and Environment, Wollongong 2005, New South Wales, Australia.
⁶ Faculty of Science, Sydney School of Veterinary Science, The University of Sydney, Camperdown, Sydney 2006, NSW, Australia. Electronic address: damien.higgins@sydney.edu.au.

PMID: 37977420
DOI: 10.1016/j.meegid.2023.105527

Abstract

In ruminants infected with Chlamydia pecorum, shorter lengths of coding tandem repeats (CTR) within two genes, the inclusion membrane protein (incA) and Type III secretor protein (ORF663), have been previously associated with pathogenic outcomes. In other chlamydial species, the presence of a chlamydial plasmid has been linked to heightened virulence, and the plasmid is not ubiquitous in C. pecorum across the koala's range. We therefore investigated these three markers: incA, ORF663 and C. pecorum plasmid, as potential indicators of virulence in two koala populations in New South Wales with differing expression of urogenital chlamydiosis; the Liverpool Plains and one across the Southern Highlands and South-west Sydney (SHSWS). We also investigated the diversity of these loci within strains characterised by the national multi-locus sequence typing (MLST) scheme. Although CTR lengths of incA and ORF663 varied across the populations, they occurred only within previously described pathogenic ranges for ruminants. This suggests a relatively short-term host-pathogen co-evolution within koalas and limits the utility of CTR lengths for incA and ORF663 as virulence markers in the species. However, in contrast to reports of evolution of C. pecorum towards lower virulence, as indicated by longer CTR lengths in ruminants and swine, CTR lengths for ORF663 appeared to be diverging towards less common shorter CTR lengths within strains recently introduced to koalas in the Liverpool Plains. We detected the plasmid across 90% and 92% of samples in the Liverpool Plains and SHSWS respectively, limiting its utility as an indicator of virulence. It would be valuable to examine the CTR lengths of these loci across koala populations nationally. Investigation of other hypervariable loci may elucidate the evolutionary trajectory of virulence in C. pecorum induced disease in koalas. Profiling of virulent strains will be important in risk assessments for strain movement to naïve or susceptible populations through translocations and wildlife corridor construction.

Keywords: Chlamydia pecorum; Koala; ORF663; Virulence; incA.

MeSH terms

Animals
Chlamydia Infections* / veterinary
Chlamydia* / genetics
Genetic Markers
Multilocus Sequence Typing
Phascolarctidae* / genetics
Ruminants
Swine
Virulence / genetics

Substances

Genetic Markers

Supplementary concepts

Chlamydia pecorum