The prevalence of salmonella, yersinia and mycobacteria in slaughtered pigs in Switzerland

Clinically healthy food animals can be reservoirs for various foodborne pathogens. In general, such animals do not have lesions that are visible during meat inspection. Pigs are considered to be carriers of salmonella, yersinia and mycobacteria, but the risk of transmission to humans is difficult to assess. The aim of this study was to estimate the actual prevalence of the three above mentioned pathogens in the Swiss pig population and to comment on their significance. A total of 570 samples each of tonsils and mesenteric lymphnodes, were collected at two slaughterhouses from carcasses of apparently healthy pigs and analyzed for the presence of salmonella, yersinia and mycobacteria. The prevalence of salmonella (0.9%) was found to be lower than--while that of yersinia (8.1%) and mycobacteria (12.8%) about equal to--results reported from other European countries. Yersinia typing showed that serotype O:9 of Yersinia enterocolitica (2.5%) was 6 to 7 times more frequent than serotype O:3 (0.4%)--formerly the most frequent serotype. Mycobacterium avium was the most frequent isolate (90.7%) among the mycobacteria isolated. Although all three pathogens are present in the Swiss pig population, we consider the risk of transmission to humans via consumption of pork as low. Appropriate preventive measures and quality management should contribute to keep the risk under control.