Testing of pathogenic Yersinia enterocolitica in pig herds based on the natural dynamic of infection.

This study was performed to evaluate testing methods of pathogenic Yersinia enterocolitica in pigs at different ages. Relevant tools and procedures are crucial if pig herds should be declared free from pathogenic Y. enterocolitica. Historical data based on serology showed that the two farms investigated in this study (herds A and B) were contaminated with Y. enterocolitica O:3 since at least 1995. Laboratory investigations of 60 pigs were sampled one to four times (herd A) and 20 pigs were sampled one to three times (herd B) at different ages were the basis for this report. The following testing procedures could be used to conclude that a herd is free from pathogenic Y. enterocolitica:--serological testing of pigs could be performed as a basis for categorisation for all ages from about 100 days including at slaughter when the pigs are 150-180 days old, --bacteriological examination of faeces could be used as a basis for categorisation at all ages from 85 days until about 135 days, --bacteriological examination of tonsils could be used as a basis for categorisation at all ages from 85 days including at slaughter when the pigs are 150-180 days old. However, due to animal welfare aspects, one should avoid sampling of tonsils. Accordingly, the serological method or bacteriological examination of faeces at relevant ages should be preferred. One aspect related to slaughter hygiene is that in pigs slaughtered at the age of 135 days or more, the tonsils may be a more significant source of human pathogenic Y. enterocolitica than faeces.