Salmonella choleraesuis in swine: carrier state studies

The purpose of these studies was to investigate the carrier state of Salmonella choleraesuis in swine. Pigs were infected with S. choleraesuis intranasally or by gastric route. At 2, 4 and 6 weeks post inoculation intranasally infected pigs had more positive tissues; however, at 12 weeks post inoculation no differences were observed. Regardless of route of inoculation, S. choleraesuis can most often be recovered from the ileocolic junction, ileocolic lymph node, fecal contents, tonsil, lung and colon. A carrier state was maintained for at least 12 weeks in both groups. Humoral and mucosal antibody titers as well as cellular immune responses to S. choleraesuis antigens were observed for both groups;In another study, pigs were infected with 10[superscript]9, 10[superscript]6 or 10[superscript]3 CFU of S. choleraesuis (high, medium and low dose, respectively). Pigs given a high dose remained positive throughout the 15 week experiment. The medium dose group had a persistent infection for at least 9 weeks. In contrast, S. choleraesuis was not recovered at any time point from the low dose group. Humoral immune responses were dose dependent. No cellular immune response was observed after a low dose while optimal antigen-specific responses were observed after the medium dose. A lower lymphocyte blastogenic response was observed in the high dose group in response to S. choleraesuis endotoxin and concanavalin A indicating that some level of lymphocyte immunosuppression occurred after the high dose challenge;The natural transmission of S. choleraesuis in swine was also studied. Group 1 (n = 12) was challenged with 10[superscript]8 S. choleraesuis by intranasal inoculation. One day post inoculation (PI) group 2 (n = 24) was commingled with group 1. Pigs in group 1 were shedding 2.61 log[subscript]10 CFU/g feces prior to commingling. The data indicated that group 2 pigs were shedding S. choleraesuis 24 hours after commingling. At 1 week PI 32/32 group 1 tissues were positive for S. choleraesuis while 39/62 tissues were positive for group 2. At 12 weeks PI only group 2 had positive tissues. These data indicate that naive swine exposed to swine shedding a relatively low level of S. choleraesuis can be infected with and shed S. choleraesuis within 24 hours of exposure. However, under well managed conditions, the level of S. choleraesuis can be significantly reduced in naturally exposed swine