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Appl. Environ. Microbiol., 01 1996, 141-146, Vol 62, No. 1
JT Gray, PJ Fedorka-Cray, TJ Stabel and TT Kramer
This experiment was designed to study the natural transmission of
Salmonella choleraesuis in swine. Forty pigs were divided into three
groups. Group 1 (n = 12) was challenged with 10(8) CFU of S. choleraesuis
per ml by intranasal inoculation. One day postinoculation (p.i.), group 2
(n = 24) was commingled with group 1. Group 3 (n = 4) served as
uninoculated controls. Serum samples were collected weekly. Blastogenesis
assays and necropsies were performed at 1, 2, 4, 6, 9, and 12 weeks p.i.,
and 16 tissue samples per pig were collected and cultured. Environmental
(pooled feces from the pen floor) levels of S. choleraesuis were 2.61 log10
CFU/g of feces at 24 h p.i. (immediately prior to commingling). Severe
clinical signs were observed in groups 1 and 2. The results indicated that
at least 16% of group 2 pigs were shedding S. choleraesuis within 24 h of
commingling. At 1 week p.i., 32 of 32 group 1 and 39 of 62 group 2 tissue
samples were positive for S. choleraesuis. Only 3 of 12 group 2 pigs were
positive at 6, 9, and 12 weeks (1 pig for each week), indicating that only
a small proportion of infected swine become long-term carriers. At 12 weeks
p.i., only the colon and colonic lymph node samples of one pig from group 2
were positive. Humoral, mucosal, and cellular immune responses were similar
between groups 1 and 2. These data demonstrate that a few pigs shedding low
levels of Salmonella organisms before slaughter can result in rapid
transmission and subsequent shedding by many swine.
Copyright © 1996, American Society for Microbiology
Natural transmission of Salmonella choleraesuis in swine
USDA-Agricultural Research Service-National Animal Disease Center, Ames, Iowa 50010, USA.
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