Siobhon Egan

Ticks (Ixodida) represent one of the most important vector groups affecting human and animal health, and in recent years there have been increasing concerns regarding the cause of tick-borne disease affecting Australians. Worldwide, wildlife health surveillance is recognised as a key tool for investigating tick-borne infections and a One Health approach is essential to understand the epidemiology of tick-associated microbes. Therefore, this research aimed to; i) identify ticks from Australian wildlife; ii) investigate bacteria and haemoprotozoa present in wildlife and ticks; and iii) characterise microbes and understand the interplay between host-microbetick. Molecular tools were used to assist in the identification of Australian ticks. Museum specimens of the human biting tick Amblyomma triguttatum were used to investigate the molecular systematics of this species complex. A set of molecular barcodes was developed for Australian ticks, which was important for the accurate identification of immature life stages and cryptic species. Additionally, a novel 12S rDNA metabarcoding assay was developed for high throughput identification of ticks. Free-ranging animals and their ticks were sampled from urban and periurban areas. The bacterial and haemoprotozoan diversity was characterised using a combination of amplicon high-throughput sequencing, targeted Sanger sequencing, and microscopy. Bacterial profiling generated over 100 million sequences. Statistical analysis using constrained ordination methods revealed blood, tick and tissues had distinct community signatures. A diverse range of tick associated microbes was identified, such as Anaplasmataceae, Bartonellaceae, Borreliaceae, Coxiellaceae, Midichloriaceae. Overall, these microbes were rare in wildlife hosts and generally confined to specific sample types. In addition, eight species of haemoprotozoa were identified, including species within the genera Babesia, Hepatozoon, Theileria and Trypanosoma. Lastly, this study further confirmed the absence of northern hemisphere tick-borne pathogens and provided further evidence of the unique microbes present in Australian wildlife and ticks.

Molecular methods have recently revealed novel organisms inhabiting native Australian ticks, some of which are potentially pathogenic due to their similarity to causes of known tick-borne diseases (TBDs) worldwide. Australian bandicoots (Order: Peramelemorphia) are hosts of ticks that are known to bite humans. The persistence of bandicoots in urban and peri-urban areas results in increased exposure of humans to bandicoot ticks, and the bacterial diversity of ticks parasitising bandicoots is therefore of public health interest and requires further investigation. This study analysed 290 ticks parasitising bandicoots from New South Wales (NSW; n = 125), Queensland (QLD; n = 26), Northern Territory (NT; n = 15), Tasmania (TAS; n = 80), and Western Australia (WA; n = 44). A total of seven tick species (Haemaphysalis bancrofti, H. humerosa, Ixodes australiensis, I. fecialis, I. holocyclus, I. myrmecobii and I. tasmani) were identified from four Australian bandicoot species; the eastern barred bandicoot (Perameles gunnii), the long-nosed bandicoot (P. nasuta), the northern brown bandicoot (Isoodon macrourus), and the southern brown bandicoot (I. obesulus). Next Generation Sequencing (NGS) targeting the ubiquitous bacterial 16S rRNA gene was applied to a sub-sample of ticks (n = 66). Analysis of sequence data revealed the presence of Anaplasma, Borrelia, Ehrlichia and ‘Ca. Neoehrlichia’. Anaplasma bovis was detected in two ticks (H. bancrofti and H. humerosa) from the same bandicoot in NSW. A likely novel Ehrlichia sp. was identified from a single I. fecialis tick in WA. In addition to the confirmation of the recently described ‘Ca. Neoehrlichia arcana’ and ‘Ca. N. australis’ inhabiting I. holocyclus and I. tasmani from NSW and QLD, a novel ‘Ca. Neoehrlichia’ species was detected in ticks (I. australiensis and I. fecialis) from WA. Furthermore, sequences 98.8% similar to ‘Ca. Borrelia tachyglossi’ provide the first molecular description of Borrelia inhabiting ticks (H. humerosa and I. tasmani) parasitising Australian bandicoots. This study has provided an interesting insight into the microbial communities present in ticks parasitising Australian bandicoots and raises questions about the potential for tick-associated illness in people parasitised by these ticks. An investigation into the characterisation, prevalence, pathogenicity and transmission dynamics of these candidate tick-borne pathogens is required to establish the significance of this study.