Submitted to: United States Animal Health Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/1/1995
Publication Date: N/A
Technical Abstract: The natural transmission of Salmonella choleraesuis in swine was investigated. Forty pigs were divided into 3 groups. Group 1 (n=12) was challenged with 10**8 S. choleraesuis by intranasal inoculation. One day postinoculation (PI) group 2 (n=24) was commingled with group 1. Group 3 served as uninoculated controls. Serum was collected weekly, blastogenesis assays and necropsies were performed at 1, 2, 4, 6, 9 and 12 wk PI. Environmental levels of S. choleraesuis were 2.61 log10 CFU/g feces prior to commingling. Severe clinical signs were observed in group 1 and group 2. Results indicated that at least 16% of group 2 pigs were shedding S. choleraesuis within 24 h after commingling. At 1 wk PI, 32/32 group 1 and 39/62 group 2 tissues were positive for S. choleraesuis. Only 3/12 group 2 pigs were S. choleraesuis-positive at 6, 9, and 12 wk, indicating that only a small population of swine will become long-term carriers. At 12 wk PI, only group 2 pigs had positive tissues. Humoral, mucosal and cellular immune responses were similar between groups 1 and 2. These data demonstrate that the rate of natural transmission of S. choleraesuis is rapid and suggest that few pigs shedding relatively low levels of Salmonella before slaughter can result in rapid transmission and subsequent shedding of the pathogen by many swine. Additionally, under natural conditions the infective dose is much lower than those required for experimental infections and low levels of Salmonella in the environment can infect naive populations of swine.