Transmission of Salmonella in dairy herds quantified in the endemic situationGerdien Van Schaika, Don Klinkenbergb, Jan Velinga and Arjan Stegemanb
a Animal Health Service Ltd, PO Box 9, 7400AA Deventer, The Netherlands
b Department of farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, The Netherlands
(Received 7 September 2006; accepted 6 June 2007 ; published online 20 September 2007)
Abstract - Salmonella is a cause of concern in the cattle industry, because it is a zoonosis causing severe invasive infections in humans and because it causes economic and welfare losses in infected herds. In general, cattle in the Netherlands are infected with two types; Salmonella Dublin and Salmonella Typhimurium. Both types cause clinical signs but S. Dublin outbreaks are more prevalent and clinical signs are more severe than S. Typhimurium outbreaks. Our knowledge of the transmission of Salmonella within herds is still limited, while this is an essential component for modelling the success of intervention strategies to control Salmonella. The aim of our study was to estimate the basic reproduction ratio (R0), the number of secondary cases produced from each primary case in a totally susceptible population, for S. Dublin and S. Typhimurium in dairy herds. Serological data were obtained from eight farms with a clinical outbreak of Salmonella, two with an outbreak of S. Dublin and 6 of S. Typhimurium. R0 was estimated from the serological data of the herds that were in an endemic state of the infection. R0 across herds was estimated to be 2.5 (95% CI 1.7-9.8) and 1.3 (95% CI 1.1-1.7) for S. Dublin and S. Typhimurium, respectively. The between herd variation was significant and fairly large. The results of the sensitivity analysis showed that the R0 estimate was not sensitive for changes in the latent, infectious or seropositive periods. The R0 estimates indicated that the infection would not spread very extensively in susceptible populations under management systems similar to the ones in the study herds.
Key words: Salmonella Dublin / Salmonella Typhimurium / transmission / dairy cattle
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© INRA, EDP Sciences 2007