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Active disease surveillance in kangaroos utilising the commercial harvesting industry

Potter, Abbey (2011) Active disease surveillance in kangaroos utilising the commercial harvesting industry. PhD thesis, Murdoch University.

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The aim of this study was to develop a framework for disease surveillance in one of the Australia’s most abundant macropods using the kangaroo harvesting industry. The impetus for this work arose because wildlife species are considered to play a significant role in the introduction, maintenance and spread of a majority of the world’s emerging infectious diseases yet active disease surveillance is rarely undertaken in these free-ranging populations. The framework developed was trialled by collecting samples and testing them for a number of significant emerging infectious diseases, including Salmonella, Coxiella burnetii and Ross River virus (RRV).

Kangaroos have long been suspected of carrying high levels of Salmonella, yet no definitive study has been undertaken to determine the true prevalence of infection in their natural habitat. Faecal samples were collected from 645 western grey kangaroos (Macropus fuliginosus) from ten different geographical locations throughout Western Australia over a period of 18 months and cultured for Salmonella spp. The estimated prevalence in the animals surveyed was approximately 3.6%. Faecal shedding was greatest following increased periods of rainfall in the April to June quarter. The relatively low prevalence of faecal shedding suggests that kangaroos in their natural habitat support the organism but are unlikely to pose any greater risk of zoonotic infection than other domestic livestock species. Whilst kangaroos have not yet been associated with food-borne outbreaks of disease, serotypes known to cause salmonellosis were isolated in this study, such as Salmonella enterica serovar Muenchen, Kiambu and Saintpaul.

Few studies have investigated the role of macropods in the maintenance and transmission of C. burnetii. Paired faecal and serum samples were collected from approximately 1000 western grey kangaroos from across twelve locations throughout Western Australia. An indirect ELISA was used to detect C. burnetii antibodies in serum, whilst quantitative PCR was used to detect C. burnetii DNA in faecal material. The estimated seroprevalence across all sample collection sites was 24.1%, whilst C. burnetii DNA was detected in the faeces of 4.1% of animals surveyed. Seroprevalence was significantly higher following increased periods of rainfall in the 60 days prior to sample collection (p<0.05), with seroprevalence lowest in the October to December quarter. These results suggest that kangaroos are likely reservoirs of the organism in Western Australia, posing a zoonotic threat to industry workers and animal handlers.

Ross River virus is Australia’s most common mosquito-borne disease and the western grey kangaroo is suspected of being a significant vertebrate host in the southwest of Western Australia. A total of 2605 serum samples, collected from across fourteen locations throughout the state, were tested for RRV neutralising antibodies. The seroprevalence varied significantly between geographical regions but was estimated to be 44.0% across all sample collection locations. Despite difficulties associated with age-based selection bias introduced through the kangaroo harvesting industry, surveillance within western grey kangaroo populations appears to provide a means of assessing the background risk of RRV for any given location and may assist in improving the capacity to predict future RRV activity.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Biomedical Sciences
Supervisor(s): Fenwick, Stan, Reid, Simon, Johansen, C. and Lindsay, M.
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