Chlamydia are obligate intracellular bacterial pathogens of humans and animals, sharing a unique developmental cycle that relies on an intimate relationship with their host’s cells. Contrary to this specialised lifestyle, we are becoming increasingly aware that several chlamydial species have a broad host range. With new tools in development, it is also becoming clearer that cross-host transmission may form normal part of the epidemiology of these infectious diseases. In the current study, the role of Australian native animals as either reservoirs of chlamydial infection ‘spill-over’ or as the recipients of these events will be investigated, featuring recent ongoing studies of two veterinary chlamydial pathogens, Chlamydia psittaci, and Chlamydia pecorum.
For the former, fine-detailed molecular epidemiological investigations in collaboration with New South Wales Department of Primary Industries have revealed an emerging role for C. psittaci in equine abortion and zoonosis to veterinarians. Multi-locus sequence typing and genomic analysis was performed on equine C. psittaci placental samples from mares with abortions in 2014 – 2016 from New South Wales. Molecular typing results revealed that all samples appeared to be genetically identical, clustering tightly to a globally distributed and highly pathogenic subclade of this pathogen. These strains were also recently associated with zoonotic cases in the Blue Mountains suspected to be acquired through environmental contamination by C. psittaci infected birds.
Ongoing work has also highlighted the role that historical and contemporary spill-over may play in the epidemiology of koala chlamydial infections. Culture-independent genome sequencing was performed on a large collection of C. pecorum strains from (i) koalas; (ii) Australian livestock; and (iii) livestock from elsewhere. This analysis revealed that koala strains are genetically diverse, reflecting the known global diversity of C. pecorum. Clades of koala and livestock strains were also identified and some evidence that certain livestock strains are ancestral to koala lineages. The results of both studies highlight new opportunities to reduce the risk of these infectious diseases in humans and animals.