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Rickettsiales and rickettsial diseases in Australia

Izzard, Leonard (2010) Rickettsiales and rickettsial diseases in Australia. PhD thesis, Murdoch University.

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      Abstract

      Currently, there are 12 known Rickettsiales species in Australia. However research into the diversity and range of these agents in Australia is still far from complete.

      A sero-epidemiological study was undertaken around the city of Launceston in Tasmania, Australia to determine the level of exposure to spotted fever group (SFG) rickettsia among the local cat and dog population. The study showed that over 50% of the dogs and cats tested were positive for SFG rickettsiae antibodies. However, no correlation was observed between the animals’ health and seropositivity at the time of testing.

      Ixodes tasmani ticks collected from Tasmanian devils in Tasmania were tested for the presence of SFG and typhus group (TG) rickettsiae using a specific real time PCR (qPCR), and 55% were found to be positive. The gltA, rompA, rompB and sca4 genes were then sequenced. Using the current criteria this new rickettsia qualified as a Candidatus species, and was named Candidatus Rickettsia tasmanensis, after the location from which it was first detected.

      Soft ticks of the species Argas dewae were collected from bat roosting boxes north of Melbourne. Of the ten ticks collected, seven (70%) were positive for SFG rickettsiae using the qPCR mentioned above. An isolate was obtained using cell culture isolation methods and the rrs, gltA, rompA, rompB and sca4 genes were sequenced. Using the current criteria this new rickettsia qualified as a novel species, and was tentatively named Rickettsia argasii sp. nov. after the tick genus from which it was isolated.

      Four family members and their neighbour living in metropolitan Victoria became ill after exposure to a flea-infested kitten. Initial serological analysis indicated a typhus group (TG) rickettsial infection. However, testing of fleas from the group of cats in Lara, Victoria, where the kitten originated, revealed the presence of R. felis, the agent of cat flea typhus. This was the first case of human infection with R. felis in Australia and the first detection of R. felis in fleas in Victoria.

      A tourist returning to Australia from the United Arab Emirates was diagnosed with a scrub typhus group (STG) rickettsial infection and the agent was isolated from their blood. Analysis of the rrs and 47kDa genes showed significant divergence compared to all available strains of Orientia tsutsugamushi. Due to the degree of genetic divergence and the geographically unique origin of this isolate it was considered to be a new species, which has been tentatively named Orientia chuto, with ‘chuto’ being Japanese for ‘Middle East’.

      Dogs in central and northern Australia were tested for Anaplasma platys using a specifically designed real-time PCR (qPCR) assay. Of the 68 dogs tested, 27 (40%) were positive for A. platys DNA, including six dogs from Western Australia. This was the first report of A. platys in Western Australia.

      These studies offer an insight into the range and diversity of Rickettsiales and rickettsial diseases previously unrecognised in Australia.

      Publication Type: Thesis (PhD)
      Murdoch Affiliation: School of Veterinary and Biomedical Sciences
      Supervisor: Fenwick, Stan
      URI: http://researchrepository.murdoch.edu.au/id/eprint/3888
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