In Australia, the most successful chlamydial species are the infamous koala (and sheep) pathogen Chlamydia pecorum, and Chlamydia psittaci, an emerging pathogen with zoonotic potential. Little is known about the exact host range for these pathogens, nor about infections caused by other chlamydial organisms in Australian livestock or wildlife. Considering that chlamydial organisms can be encountered by humans at the animal/human interface, or native wildlife at the domesticated animal/wildlife interface, we investigated molecular epidemiology of chlamydial organisms infecting Australian domesticated and wild animals.
We screened a catalogue of > 400 samples taken from domesticated sheep, cattle, pigs, and horses, and wild deer and range of wild psittacine and non-psittacine birds using pan-Chlamydiales as well as species-specific assays. Whole genome sequencing was performed on a subset of C. pecorum and C. psittaci positive samples from several livestock and bird hosts to evaluate genetic diversity of infecting strains.
Overall, chlamydial DNA was detected in >60% samples, including all domesticated and wildlife hosts. Sequence analyses revealed that genetically diverse novel, as well as traditional, chlamydial organisms infect an expanded range of Australian animals. Not surprisingly, we have detected new hosts for the infamous C. pecorum and C. psittaci, raising new questions regarding reservoirs for these pathogens, in addition to concerns about risks of spill-over between livestock, humans, and native wildlife1.
Whole genome molecular typing revealed that the C. psittaci strains from Australian livestock and birds are diverse, however mainly cluster in two clades: the globally distributed, highly virulent parrot ST24 clade; and pigeon-associated ST35 clade, again indicative of spill-over of C. psittaci infections from birds. In contrast, livestock C. pecorum strains clustered into a clonal ST23 clade, a genotype globally associated with sheep polyarthritis and cattle encephalomyelitis, but genetically distinct from koala strains.
Future research must expand on these molecular findings to understand the epidemiology as well as the zoonotic potential posed in association with these new reservoirs and new chlamydial infections.