Low prevalence of yadA-positive Yersinia enterocolitica in sows

Yersinia enterocolitica 4/O:3 is commonly isolated from fattening pigs in Finland, but its prevalence in sows is relatively unknown. The current study determined the prevalence of yadA-positive Y. enterocolitica in sows and fattening pigs with polymerase chain reaction (PCR) and culture methods. The strains were characterized with pulsed-field gel electrophoresis (PFGE) using NotI DNA-restriction enzyme. Pathogenic Y. enterocolitica was detected in only 14% of sow tonsils compared with 56% of tonsils of fattening pigs. The prevalence varied between seven slaughterhouses from 0% to 30% in sows and from 30% to 87% in fattening pigs. A total of 37 NotI profiles were obtained from 148 Y. enterocolitica 4/O:3 strains isolated from 134 tonsil samples: eight profiles were obtained from 26 sow strains and 34 from 122 fattening pig strains. Two types predominated in both sows and fattening pigs. The prevalence of yadA-positive Y. enterocolitica in fattening pigs increased from 1995 versus 1999; the mean prevalence in five slaughterhouses for the 2 years was 33% and 64%, respectively. Seven NotI profiles, including the two common types, were found both years. In conclusion, pathogenic Y. enterocolitica was detected at a significantly lower rate in sows than in fattening pigs. Moreover, the prevalence of this pathogen in fattening pigs was significantly higher in 1999 than in 1995. Some Y. enterocolitica 4/O:3 strains persisting among slaughter swine were demonstrated to be very stable genetically. This study shows that fattening pigs are an important reservoir of different genotypes of Y. enterocolitica 4/O:3 strains.