Enteropathogenic Yersinia in pork production

Enteropathogenic Yersinia, that is pathogenic Yersinia enterocolitica and Yersinia pseudotuberculosis, are zoonotic pathogens causing yersiniosis, the third most frequently reported zoonosis in the EU. Enteropathogenic Yersinia are frequently isolated from the tonsils and intestinal contents of pigs. Similar Y. enterocolitica genotypes have been identified both in pig and human strains and human yersiniosis has been statistically associated with the consumption of pork products in case-control studies, indicating pigs and pork products as an important source of human Y. enterocolitica infections. The link between pathogenic Y. pseudotuberculosis and pork is less clear; however, Y. pseudotuberculosis has also been isolated from carcasses and pork, indicating a possible route from pigs to humans. This work aimed at clarifing the transmission of enteropathogenic Yersinia from farm to slaughterhouse, determining factors affecting the prevalence of enteropathogenic Yersinia on pig farms, and test bagging as an intervention at the slaughterhouse. In addition, methods for the isolation of enteropathogenic Yersinia were evaluated. Isolation of enteropathogenic Yersinia from samples of animal origin is difficult and time-consuming. However, in many cases such as in outbreak investigations, isolates are needed for further typing. Of the isolation methods used, cold enrichment was efficient at isolating enteropathogenic Yersinia, whereas the sensitivity of other methods, such as direct isolation and selective irgasan-ticarcillin-potassium chlorate enrichment, for the isolation of enteropathogenic Yersinia was low. However, none of the isolation methods tested detected all the enteropathogenic Yersinia-positive samples and new isolation methods need to be developed. The transmission of enteropathogenic Yersinia from pigs to carcasses and pluck sets was investigated by collecting samples from individual ear-tagged pigs on the farm and at the slaughterhouse and by analyzing the isolated strains using pulsed-field gel electrophoresis (PFGE). Since the same PFGE types can be isolated from pigs and their subsequent pluck sets and carcasses, the main contamination source of pluck sets and carcasses at the slaughterhouse appears to be pigs that carry enteropathogenic Yersinia from farms to the slaughterhouse. However, since non related genotypes could also be isolated from carcasses and pluck sets, the slaughterhouse environment and tools can also contaminate carcasses and pluck sets. The high prevalence of enteropathogenic Yersinia in pigs results in high contamination rates of pluck sets and carcasses. Therefore, interventions at the farm level can decrease the transmission of Yersinia from pigs to pluck sets and carcasses. Farm factors such as production capacity and type may affect the prevalence of enteropathogenic Yersinia on farms. Since the prevalence of pathogenic Y. enterocolitica and Y. pseudotuberculosis varies among farms, within-farm factors can affect how enteropathogenic Yersinia spreads in pigs on farms. In statistical studies, factors affecting Y. pseudotuberculosis included organic production, contacts with pest animals, and the outside environment, whereas the high prevalence of pathogenic Y. enterocolitica was associated with factors such as high production capacity and conventional production. The epidemiology of pathogenic Y. enterocolitica and Y. pseudotuberculosis appears to be different on pig farms and this difference needs to be addressed if interventions on pig farms are considered. However, further information on the factors affecting the prevalence of enteropathogenic Yersinia on pig farms is needed before interventions at the farm level can be used. The effect of bagging of the rectum was studied by sampling tonsils, intestinal content, and carcasses with and without bagging of the rectum and constructing a Bayesian hidden variable model. According to the model, bagging of the rectum reduced significantly the contamination of carcasses at the slaughterhouse. However, since after bagging the prevalence of pathogenic Y. enterocolitica in different parts of the carcass was relatively high, 4–14%, other interventions are also needed. Most of the positive carcass samples were head and chest swabs, indicating that tonsils may be the contamination source.