Abstract
BackgroundMembers of the order Chlamydiales are known for their potential as human and veterinary bacterial pathogens. Despite this recognition, epidemiological factors such as routes of transmission are yet to be fully defined. Ticks are well known vectors for many other infections with several reports recently describing the presence of bacteria in the order Chlamydiales in these arthropods. Australian wildlife are hosts to an extensive range of tick species. Evidence is also growing that the marsupial hosts these ticks parasitise can also be infected by a number of bacteria in the order Chlamydiales, with at least one species, Chlamydia pecorum, posing a significant conservation threat. In the current study, we investigated the presence and identity of Chlamydiales in 438 ixodid ticks parasitizing wildlife in Australia by screening with a pan-Chlamydiales specific targeting the 16S rRNA gene.ResultsPan-Chlamydiales specific PCR assays confirmed the common presence of Chlamydiales in Australian ticks parasitising a range of native wildlife. Interestingly, we did not detect any Chlamydiaceae, including C. pecorum, the ubiquitous pathogen of the koala. Instead, the Chlamydiales diversity that could be resolved indicated that Australian ticks carry at least six novel Chlamydiales genotypes. Phylogenetic analysis of the 16S rRNA sequences (663 bp) of these novel Chlamydiales suggests that three of these genotypes are associated with the Simkaniaceae and putatively belong to three distinct novel strains of Fritschea spp. and three genotypes are related to the “Ca. Rhabdochlamydiaceae” and putatively belong to a novel genus, Rhabdochlamydia species and strain, respectively.ConclusionsSequence results suggest Australian wildlife ticks harbour a range of unique Chlamydiales bacteria that belong to families previously identified in a range of arthropod species. The results of this work also suggest that it is unlikely that arthropods act as vectors of pathogenic members of the family Chlamydiaceae, including C. pecorum, in Australian wildlife. The biology of novel Chlamydiales identified in arthropods remain unknown. The pathogenic role of the novel Chlamydiales identified in this study and the role that ticks may play in their transmission needs to be explored further.
Highlights
Members of the order Chlamydiales are known for their potential as human and veterinary bacterial pathogens
Tick species identified from Australian wildlife Overall, 438 adult female engorged ixodid ticks comprised of seven species were identified from ten marsupial hosts and one monotreme host species
Novel Chlamydiales genotypes were detected in a screen of 438 native Australian ticks
Summary
Members of the order Chlamydiales are known for their potential as human and veterinary bacterial pathogens. Evidence is growing that the marsupial hosts these ticks parasitise can be infected by a number of bacteria in the order Chlamydiales, with at least one species, Chlamydia pecorum, posing a significant conservation threat. While within-host routes of transmission are reasonably well characterised for members of the family Chlamydiaceae, much less is known about the transmission of bacteria in other chlamydial families or how cross-host transmission events occur for these pathogens For the latter, direct contact with infected animals is a risk factor for zoonotic transmission of C. psittaci [13] and Chlamydia abortus [14] while indirect contact via environmental contamination from infected animals is suspected for the former species [15]. Other potential routes of transmission including the use of vectors are largely unknown
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