Lurette Amandine, Belloc Catherine, Touzeau Suzanne, Hoch Thierry, Ezanno Pauline, Seegers Henri, Fourichon Christine
INRA, UMR1300 Unité Bio-Agression, Epidémiologie et Analyse de Risque, BP 40706, F-44307 Nantes, France.
Vet Res. 2008 Sep-Oct;39(5):49. doi: 10.1051/vetres:2008026. Epub 2008 Jun 14.
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.
将感染猪送往屠宰场是猪肉受细菌危害污染从而威胁人类健康的主要来源。我们提出了一个沙门氏菌在从产仔到育肥猪群中传播的模型，假设感染猪的流行率取决于猪的整个生命周期和生长过程。这个随机离散时间模型既代表了采用批次管理的从产仔到育肥猪群的种群动态，也代表了沙门氏菌的传播。模型考虑了四种相互排斥的个体健康状态：无沙门氏菌、血清学阴性排菌者、血清学阳性排菌者和血清学阳性非排菌携带者，以此区分血清学阳性动物和排菌者。由于间接传播是主要传播途径，感染概率取决于猪环境中沙门氏菌的数量（Q）。使用了一个剂量效应函数，有两个阈值，假设高Q时暴露饱和，低Q时暴露最低。沙门氏菌被引入一个初始无沙门氏菌的150头母猪群中。计算不同批次母猪和猪以及由不同批次猪组成的待交付猪群中排菌者的流行率和血清学阳性率随时间的变化情况。该模型显示，在猪群中，不同交付组之间以及不同重复实验中，血清学阳性率随时间变化差异很大。平均血清学阳性率和平均排菌流行率分别为19.3%和13.8%。敏感性分析表明，排出的沙门氏菌数量和母体保护因子是影响待交付猪中沙门氏菌流行率的最具影响力的参数。
