Introduction of infected animals to herds is an important route for the spread of Yersinia enterocolitica infection between pig farms.

Altogether, 369 pathogenic Yersinia enterocolitica isolates from 1,118 fecal samples collected from 22 pig farms of different production types were characterized by biotyping, serotyping, and genotyping using multiple-locus variable-number tandem repeats analysis. We investigated the distribution of the different genotypes at the farm level and their association with different farm conditions. Pigs were found to carry and transmit Y. enterocolitica between farms, because the same genotypes were found on farms that had previously transported the pigs between them. The purchase of new animals for the farms associated significantly with the number of different multiple-locus variable-number tandem repeats analysis types of Y. enterocolitica found within a farm. Some genotypes seemed to persist on farms for years. The results of this study show that pigs purchased from infected herds transmit Y. enterocolitica infection between farms. Certain pig farms may act as long-term sources of infection.