Infectivity and persistence of an outbreak strain of Salmonella enterica serotype Typhimurium DT160 for house sparrows (passer domesticus) in New Zealand

AIM: To examine the infective dose, incubation period and disease progression of an isolate of Salmonella enterica serotype Typhimurium definitive type 160 (DT160) originating from a naturally-infected house sparrow (Passer domesticus) during an outbreak of the disease in New Zealand.METHODS: Thirty-six house sparrows captured from the wild and free of Salmonella spp were divided into six groups of six birds, housed individually, and inoculated orally with phosphate buffered saline (PBS) or 10, 100, 1000, 100000, 2 × 100000000 colony forming units (cfu) of the outbreak strain of S. Typhimurium DT160. The birds were observed for 10 days for clinical signs and/or mortality, and faecal samples were collected to determine excretion of S. Typhimurium. The birds were euthanised 11 days post-inoculation (p.i.) and a wide range of tissue samples were collected for histopathological examination, and culture and typing of Salmonella spp. Macro-restriction profiling by pulsed-field gel electrophoresis (PFGE) using XbaI was performed for the epidemiological typing of S. TyphimuriumDT160 isolates.RESULTS: Mortality in house sparrows inoculated with S. Typhimurium DT160 was dose-dependent, and 2/6 birds inoculated with 100000 cfu and all six birds inoculated with 2 × 100000000 cfu died during the study. Infected sparrows displayed few clinical signs, apart from diarrhoea and/or polyuria, fluffed plumage, and sitting on the floor of the cage. Faecal excretion of DT160 occurred briefly in two birds inoculated with 100 cfu and four birds inoculated with 1000 cfu, on most days in five birds inoculated with 100000 cfu, and continuously in six birds inoculated with 2 × 100000000 cfu. DT160 was isolated from the livers of three birds which received 1000 cfu, five birds dosed with 100000 cfu, and all six birds given 2 × 100000000 cfu. Following necropsy, histopathological lesions similar to those seen in the natural disease were observed in the liver or spleen of thebirds which received 1000 cfu, and all birds dosed with '100000 cfu.CONCLUSION: The results indicate that an isolate of S. Typhimurium DT60 originating from house sparrows in New Zealandis pathogenic to these birds and that the response is dose dependent. The persistence and excretion of the pathogen maylast for at least 10 days. This confirms that sparrows infected with DT160 could be a source of infection to humans and other in-contact animals.