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An investigation of Coxiella burnetii and Coxiella-like bacteria in the brown dog tick (Rhipicephalus sanguineus)

Greay, Telleasha (2014) An investigation of Coxiella burnetii and Coxiella-like bacteria in the brown dog tick (Rhipicephalus sanguineus). Honours thesis, Murdoch University.

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There are a wide variety of animal reservoirs of the zoonotic bacterium Coxiella burnetii (C. burnetii), and ticks may play a significant role in the natural transmission cycle of this pathogen. Recently, domestic dogs have been implicated as reservoirs of C. burnetii. Dogs are the primary hosts of Rhipicephalus sanguineus (R. sanguineus), and C. burnetii has previously been detected in these ticks. The objectives of this study were to identify and record R. sanguineus ticks collected from dogs in Australia, and to investigate the prevalence of C. burnetii in these ticks. Subsequent to this, the bacterial microbiome of R. sanguineus ticks was investigated. The IS1111a transposase element gene was targeted using qPCR to detect C. burnetii DNA in R. sanguineus. The Ion Torrent™ Next-Generation Sequencing platform was used to sequence bacterial 16S rDNA in the ticks. In this study, 2,577 R. sanguineus ticks were morphologically identified and recorded in the Northern Territory, South Australia and Western Australia. There was no positive detection of C. burnetii in a subset of 31 R. sanguineus ticks by qPCR. Next-generation sequencing of the universal bacterial 16S rRNA gene revealed that a Coxiella sp. was present in 53/59 (90%) tick pools. The sequences were compared to GenBank submissions and a 100% match was obtained to a Coxiella sp. from R. sanguineus in the Philippines. A phylogenetic analysis of this Coxiella sp. showed that it does not group with the pathogenic C. burnetii. This Coxiella sp. may be a non-pathogenic endosymbiont of R. sanguineus, and future investigations could aim to assess the role of Coxiella endosymbionts in R. sanguineus, and whether this bacterium causes cross-reactivity in immunologic assays used for the diagnosis of Q fever in people.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor: Irwin, Peter and Oskam, Charlotte
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