Molecular characterisation of chlamydial infections in native Australian marsupials and their parasitising tick species

Delaney Burnard

doi:10.25907/00647

Chlamydial infections in Australia are highly prevalent in the iconic koala marsupial as well as livestock, with little known in regards to their prevalence and diversity in other native Australian marsupial species. Few marsupial species have been identified to carry novel Chlamydiae as well as Chlamydia pecorum, suggesting they may be a reservoir of infection for the koala. Furthermore, alternate routes of transmission for chlamydial species remain unexplored. An abundance of Chlamydiae diversity has recently been identified in European tick species, suggesting they may be a vector of infection. Despite these findings, almost nothing is known with regards to the genomic diversity of tick Chlamydiae and the role they play in their tick vector. Australian tick species are also known to transmit other severe bacterial diseases and yet the genetic relationships of tick vectors in Australia remain unexplored. This thesis aimed to identify the prevalence and diversity of Chlamydiae in tick species parasitising Australian wildlife and their potential as a vector for infection. Over 400 ticks were removed from several wildlife hosts in areas where C. pecorum infection rates are high and a large scale Chlamydiales-specific PCR screen was then performed. An overall prevalence rate of 79.8% in Australian parasitising tick species was identified, which was significantly higher than European prevalence rates. Interestingly, only novel genotypes were identified from the Rhabdochlamydiaceae and Simkaniaceae families, with one Rhabdochlamydiaceae genotype accounting for 50% of the chlamydial diversity. Furthermore, no C. pecorum was detected in these tick species. This first chlamydial screen of Australian parasitising tick species suggests ticks are not a vector of C. pecorum infections in Australia, yet carry an abundance of novel Chlamydiae that should be further explored considering their vector potential. This thesis also aimed to identify the presence, diversity and host range of chlamydial infections in non-koala marsupials and assess their role as a potential reservoir of C. pecorum infections in the koala. The first large scale Chlamydiales-specific PCR screen was performed on over 200 marsupials. A total of 11 species, from four Australian states including koala and non-koala habitat were screened. The overall prevalence rate of chlamydial infections in non-koala marsupials was 48%. A novel and previously described C. pecorum genotype were identified a low prevalence, suggesting they are not reservoirs of koala C. pecorum infections. In addition to several novel marsupial Chlamydiae genotypes having significant overlap with those identified in Australian tick species, one Rhabdochlamydiaceae genotype was identified in all regions of Australia sampled. This particular genotype was identical to one identified in Australian tick species, suggesting ticks may transmit specific Chlamydiae to and from marsupials.

Molecular characterisation of chlamydial infections in native Australian marsupials and their parasitising tick species

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