Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: May 23, 1996
Publication Date: N/A
Technical Abstract: Carrier state studies with Salmonella typhimurium in animals other than swine have suggested that persistence may be dose-dependent. For our studies, 19 pigs were divided into 4 groups housed in separate isolation facilities. Groups 1 (n=5), 2 (n=5) and 3 (n=5) were inoculated intranasally with 10**9, 10**6 and 10**3 CFU of S. choleraesuis, respectively. Group 4 (n=4) served as uninoculated control pigs. Clinical signs were monitored and tonsil, nasal, rectal swabs and fecal samples were collected for bacteriology. Pigs were necropsied at 6, 10 or 15 wk postinoculation (PI). Clinical signs were severe in group 1 and mild in group 2. No clinical signs were observed for group 3. Fecal shedding was dose dependent for groups 1 and 2. S. choleraesuis was not recovered from tonsil, nasal or rectal swabs, fecal samples or tissues of group 3 pigs. For pigs in group 2, fecal shedding continued through wk 9 PI and the ileocolic lymph node was positive at 6 wk PI. Group 1 continued to have positive feces and tissues through 15 wk PI. The tonsils of group 1 pigs had the highest numbers of S. choleraesuis at 15 wk PI (3.16 log10/g). Low serum IgG and IgM titers to S. choleraesuis LPS were observed for group 3 while high serum IgG and IgM titers to LPS and soluble antigen were observed for groups 1 and 2. Lymphocyte blastogenesis assays indicated a proliferative response in groups 1 and 2 in response to S. choleraesuis endotoxin. However, some level of lymphocyte immunosuppression occurred in the group 1 pigs. Control pigs were negative for all parameters. The results indicate that persistence, shedding and immune response is dose-dependent and high doses (greater or less than 10**9 CFU) result in a long-term carrier state.