The pathogenicity of Yersinia enterocolitica for piglets.

The pathogenicity of Yersinia enterocolitica, a bacterium that has been isolated frequently from healthy swine, was studied in piglets by oral challenge of two litters, one derived by cesarean section and deprived of colostrum, and the other delivered at full-term. Eight cesarean-derived piglets were divided into groups of two and challenged with four serotypes of Y. enterocolitica (O:8, O:21, O:3, O:13). Two deaths occurred and two piglets were killed because of severe illness before termination of the experiment eight days after challenge. Surviving piglets showed no clinical signs of illness. Rectal cultures were consistently positive and all cesarean-derived piglets were colonized in the small intestine and throat at necropsy. Full-term piglets were allowed access for 36 hours to sow colostrum containing low levels of antibody against the challenge strains. Six full-term piglets challenged with three serotypes of Y. enterocolitica (O:8, O:21, O:13) survived for 15 days without any signs of illness. These piglets had fewer positive rectal cultures and showed less extensive colonization of internal organs at necropsy than did cesarean-derived piglets. It is uncertain whether this increased resistance to infection with Y. enterocolitica resulted from colostrum-derived antibody, intestinal colonization with other bacteria, or an improved physical condition which accompanied full-term development. Nevertheless, the results of this challenge experiment suggest that piglets are capable of restricting colonization by Y. enterocolitica to the throat and intestinal tract without development of serious illness.