Salmonella in Free-Ranging Quokkas (Setonix brachyurus) from Rottnest Island and the Mainland of Western Australia

SIMPLE SUMMARY: Quokkas are small kangaroo-like mammals that are native to Western Australia. They live on Rottnest Island, where they are habituated to human contact, and they also live in forest environments on the mainland, where they are rarely in contact with people. It is known that quokkas can be infected with Salmonella. Salmonella is a type of bacterium that can result in diarrhoea and other signs of disease. It is known that animals can infect people with Salmonella. Many animals infected with Salmonella get sick after acquiring the infection. We collected faeces from 92 quokkas; 71 from Rottnest Island and 21 from mainland Western Australia. We detected Salmonella in almost half of the animals from Rottnest and only one animal from the mainland. We also examined the blood of these quokkas and found evidence that some of these infected quokkas had signs of mild disease that are consistent with a Salmonella infection. Our study revealed some new types of Salmonella in these quokkas. ABSTRACT: Salmonella is a genus of Gram-negative, motile, and facultative anaerobic bacteria with a worldwide distribution that contaminates multiple substrates (vegetation, food, soil, and water) and inhabits the gastrointestinal tract of birds, reptiles, and mammals, including humans. Rottnest Island is a popular tourist destination and is abundantly inhabited by quokkas (Setonix brachyurus), a charismatic small wallaby. Current data on the association between Salmonella and quokkas on Rottnest Island are outdated by approximately 30 years. Additionally, previous studies on quokkas on this island and mainland Western Australia did not perform physical examinations or any diagnostic tests. The aim of the project was to assess the prevalence of Salmonella spp. in quokkas from Rottnest Island and mainland Western Australia and correlate the presence of the bacterium with the health of the animal. Ninety-two quokkas from Rottnest Island (n = 71) and populations on the mainland (n = 21) were screened for Salmonella, and a prevalence of 47.9% and 4.8%, respectively, was determined. A total of 16 serovars were identified from 37 isolates; five of these serovars had previously not been described in the quokka. Salmonella appeared to have an effect on the haematology and blood chemistry of quokkas on Rottnest Island consistent with subclinical salmonellosis. The health of Rottnest Island quokkas, and their potential impact on the health of the visitors to the island, should continue to be monitored carefully.