How to cite this article: Vet. Res. (2008) 39:49
DOI: 10.1051/vetres:2008026

Modelling Salmonella spread within a farrow-to-finish pig herd

Amandine Lurette^{1, 2}, Catherine Belloc^{1, 2}, Suzanne Touzeau³, Thierry Hoch^{1, 2}, Pauline Ezanno^{1, 2}, Henri Seegers^{1, 2} and Christine Fourichon<sup>1, 2

1</sup>  INRA, UMR1300 Unité Bio-Agression, Épidémiologie et Analyse de Risque, BP 40706, F-44307 Nantes, France
²  ENVN, UMR1300 Unité Bio-Agression, Épidémiologie et Analyse de Risque, BP 40706, F-44307 Nantes, France
³  INRA,UR341 Unité de Mathématiques et d'Informatique Appliquées, F-78350 Jouy-en-Josas, France

Received 16 November 2007; accepted 12 June 2008; published online 14 June 2008

Abstract - Delivery of infected pigs to the slaughterhouse is a major source of pork meat contamination by bacterial hazards to humans. We propose a model of Salmonella spread within a farrow-to-finish pig herd, assuming the prevalence in infected delivered pigs depends on the whole pig life-time and growing process. This stochastic discrete-time model represents both the population dynamics in a farrow-to-finish pig herd using batch management, and Salmonella spread. Four mutually exclusive individual health states were considered: Salmonella-free, seronegative shedder, seropositive shedder and seropositive not shedding carrier, making the distinction between seropositive animals and shedders. Since indirect transmission is the main route of transmission, the probability of infection depends on the quantity of Salmonella in the pigs' environment (Q). A dose effect function is used with two thresholds, assuming saturation in exposure for high Q vs. a minimum exposure for low Q. Salmonella is introduced in an initially Salmonella-free 150-sow herd. Prevalence of shedders and seroprevalence are calculated over time in batches of sows and pigs, and in groups of delivered pigs, composed of pigs from different batches. The model shows very variable seroprevalence over time within a herd among delivered groups, as well as among replications. The mean seroprevalence and the mean shedding prevalence are 19.3% and 13.8% respectively. A sensitivity analysis shows that the Salmonella quantity shed and the maternal protective factor are the most influential parameters on Salmonella prevalence in delivered pigs.

Key words: swine / Salmonella / epidemiological model / population dynamics / environment

Corresponding author: lurette@vet-nantes.fr

© INRA, EDP Sciences 2008