Journal of the Royal Society of Western Australia, 90: 127-136, 2007 
Seasonal and spatial variation in Salmonella infections rates 
in quokkas (Setonix brachyurus) on Rottnest Island, 
Western Australia, in areas of human contact 
J.B. Iveson’S.D. Bradshaw^ & the late R.P. Hart 
" ' The Western Australian Centre for Pathology and Medical Research, 
Nedlands, Western Australia, 6009 
^ Present address: "Yoredale" 48 Paterson Road, Mt Nasura, Western Australia, 6112 
^ School of Animal Biology and Centre for Native Animal Research, 
The University of Western Australia, 
Crawley, Western Australia, 6009 
^Corresponding author: 
School of Animal Biology M092 
The University of Western Australia 
35 Stirling Highway, Crawley, Western Australia, 6009 
^ Don.Bradshaw®>u wa.edu.au 
Manuscript received October 2006; accepted June 2007 
Abstract 
A sampling programme to determine the seasonal incidence of Salmonella infections in the 
marsupial quokka, Setonix brachyurus, on Rottnest Island, was carried out in public contact areas 
over the period March 1984 to March 1985. TTie study followed an unusual rise in the frequency of 
Salmonella adclaide infections in quokkas foraging in the Thompson Bay settlement area and 
isolations from catchment waters and sewage effluent. A total of 670 tagged quokkas was swabbed 
in the island's three settlement areas, plus Kingston Barracks, Garden Lake and Lighthouse swamp. 
A total of 1,139 duplicate swab samples was collected from quokkas and 713 swabs from 244 
animals recaptured more than once. Twenty five Salmonella serotypes were identified, including 
Salmonella javiana and S. typhimurium Phage Type 202 associated with human cases previously 
traced to the island. Significant differences were found in rates of infection in quokkas and these 
peaked at approximately 40% in the resident population at Lighthouse swamp, and at 30% in 
settlement areas during the summer months. Based on population estimates, a minimum of 200 
infected animals are likely to frequent the Thompson Bay settlement area during the peak summer 
vacation period. Infection rates fell below 5% in settlement areas during the winter period but 
remained around 20% in the Lighthouse Swamp population. The majority of Salmonella infections 
in recaptured animals was classified as transient and few quokkas showed evidence of a carrier 
state, or absence of infection throughout the sampling period. Salmonella infections were higher in 
juvenile quokkas than adults in settlement areas and in adult females at Lighthouse Swamp. The 
large population density of quokkas foraging nocturnally for food in settlement areas maintained 
high levels of ground contamination with infected droppings. However, evidence of progress in 
long-term management strategies to promote natural behaviour in the island's wildlife and 
ameliorate public health problems is consistent with the absence of cases of salmonellosis traced to 
the island during the monitoring period and in subsequent years marked by significant increases 
in visitors to the island. ' 
Keywords: Salmonellosis, zoonoses, Rottnest Island, marsupial, public health 
Introduction 
Salmonella isolations from wild animals in different 
countries was reviewed in a report on serotypes 
identified by the Salmonella Reference Laboratory in the 
United Kingdom by (Taylor 1969) and recently updated 
(Anon. 2006). The possibility of infections caused by 
wildlife spilling over to humans has been highlighted in 
a recent review, (Kruse Kirkemo & Handeland 2004) 
following on early studies in Panama (Kourany Bowdre 
& Herrer 1974), Trinidad (Everard Tota Bassett & Ali 
1979), and India (Kaura & Singh 1968; Sambyal & Sharma 
© Royal Society of Western Australia 2007 
1972). In Australia, Salmonella infections acquired from 
wildlife are known to persist in non-urban aboriginal 
communities (Iveson 1983; Iveson Mackay-Scollay & 
Bamford 1969). The surprise discovery in 1972 of a major 
reservoir of Salmonella infection in the small marsupial 
wallaby Setonix braclnairus, known as the quokka, on 
Rottnest Island and the tracing of infechons in humans to 
droppings from infected animals and contamination of 
wells and water storage tanks (Iveson & Bradshaw 1973), 
alerted public health authorities to the need for improved 
preventative measures on this small island resort in 
Western Australia. The findings aLso raised questions 
concerning the management of Salmonella infections in 
wildlife populations on the island, which were first 
addressed in a Public Health report and management 
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