Globally, ticks are well known vectors of a number of pathogens, including members of the genera Anaplasma, Borrelia, Ehrlichia, Babesia, and Theileria, which are associated with a range of tick-borne diseases (TBD). These bacteria and blood-borne parasites are widely studied overseas due to their significant medical and veterinary impacts. In Australia, in recent decades, research into ticks and TBD has been focused on mammalian hosts, particularly livestock and companion animals. The relationship between wildlife and their ticks, on the other hand, are less studied. Despite disease concerns associated with ticks in Australia caused primarily by the Australian paralysis tick, Ixodes holocyclus, and other introduced species such as the bush tick, Haemaphysalis longicornis, and the brown dog tick, Rhipicephalus sanguineus, the impacts of native wildlife ticks are not known. The main objective of this thesis was to identify and characterise novel microorganisms and potential tick-borne pathogens residing in ticks that parasitise Australian wildlife.

Wildlife ticks (n= 1,000) were sourced across Australia from wildlife hospitals and sanctuaries, and genomic DNA (gDNA) was extracted from a subsample (n= 196). Following the amplification of the bacterial 16S rRNA gene V1-V2 hypervariable region, next generation sequencing (NGS) on the Illumina MiSeq platform was used to assess the microbial composition. Results revealed the presence of a Borrelia species in Bothriocroton concolor ticks collected from echidnas (Tachyglossus aculeatus), prompting further screening of additional B. concolor ticks (n= 97) using primers targeting the 16S ribosomal RNA (rRNA), flagellin (flaB), the 60 kDa heat shock protein (groEL), the glycerophosphodiester phosphodiesterase (glpQ), and the DNA gyrase (gyrB) genes. Sanger sequencing and phylogenetic analysis revealed that the Borrelia sp. identified in the B. concolor ticks was unique and distantly related to the Relapsing Fever Borrelia, with the reptile-associated (REP) Borrelia group, its sister taxa. Therefore, this novel species was described phylogenetically and named ‘Candidatus Borrelia tachyglossi’, representing the first Borrelia species to be molecularly characterised in native Australian ticks.