Salmonella infections in a marsupial, the quokka (Setonix brachyurus), in relation to seasonal changes in condition and environmental stress

Abstract

An unusual abundance of Salmonella infections was studied in an island population of a wild marsupial, the quokka (Setonix brachyurus), which experiences starvation in summer associated with significant mortality. The frequency of infections was found to vary seasonally over most parts of the island, with high infection rates (70 to 100%) in summer and low infection rates (0 to 30%) in winter. In some samples, there was an average of as many as two isolations per animal, and up to five isolations were made from a single animal. By the end of summer, virtually all animals excreted Salmonella spp., with a median rate of excretion of approximately 3,000 Salmonella organisms per g of feces. The seasonal changes occurred over intervals of only weeks. The infections are believed to be associated with disruption of the digestive physiology of the animals caused by the poor quality of feed available in summer. This conclusion was supported by a quantitative study of the infections and by a field manipulation experiment which delayed the initiation of the infections as long as a food supplement was available. The proliferation of Salmonella spp. is discussed in terms of the ecology of the quokka and of the use of Salmonella spp. as indicators of environmental stress acting on the animals.

Prevalence of Salmonella in Fecal Samples of Western Grey Kangaroos (Macropus Fuliginosus)

“…The prevalence of fecal Salmonella in this study is markedly lower than reported levels of infection in quokkas (S. brachyurus) on Rottnest Island, which peaks as high as 70-100% in summer (Iveson and Bradshaw, 1973;Hart et al, 1985). This finding can possibly be attributed to the increased exposure of quokkas to people and their waste products within a closed island population.…”

“…This finding can possibly be attributed to the increased exposure of quokkas to people and their waste products within a closed island population. During summer, when food availability is low and digestive physiology is disrupted, quokkas scavenge through food scraps left by tourists, increasing the risk of infection with Salmonella (Samuel, 1983;Hart et al, 1985).…”

“…In contrast, Eglezos et al (2007) reported statistically significant higher rates of kangaroo carcass contamination at the processor in summer. The prevalence of fecal shedding in the quokka (S. brachyurus) also peaks during summer (Hart et al, 1985). It is difficult to extrapolate the results of these studies to free-living kangaroos because the studies do not take into account the epidemiologic factors directly influencing the route of infection in mainland kangaroos in their natural habitat.…”

“…Kangaroos were first suspected of being reservoirs of Salmonella in the 1950s and 1960s following reports of contamination of kangaroo meat for export and pet food preparation (Winter, 1957;Anderson et al, 1964;Suzuki et al, 1967). The investigation of a case of salmonellosis in an infant on Rottnest Island, Western Australia showed that quokkas (Setonix brachyurus) were commonly infected with Salmonella (Iveson and Bradshaw, 1973;Hart et al, 1985). Salmonella infection is primarily a problem in captive macropods and orphaned joeys, where it can result in gastroenteritis and septicemia (Speare and Thomas, 1988;Speare et al, 1989;Thomas et al, 2001).…”

Special challenges of maintaining wild animals in captivity in Australia and New Zealand: prevention of infectious and parasitic diseases

“…These factors -together with the presence of young animals -may combine to cause overt salmonellosis. A reduction in the level of nutrition was responsible for an increased shedding rate in quokkas (Setonix brachyurus) in Western Australia (19). With the current profusion of free-ranging macropods in wildlife parks, the general public is coming into closer contact with carrier animals and some zoonotic potential therefore exists.…”