Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 7, 1997
Publication Date: N/A
Technical Abstract: A pregnant beef cow was identified as Salmonella typhimurium copenhagen (STC) fecal culture-positive and anti-Salmonella antibody-positive during a herd outbreak investigation. Serum antibodies were detected by blocking ELISA using anti-Salmonella monoclonal antibodies. The cow remained consistently fecal culture- and serologically-positive for 9 mo (8/96-4/97), even though all herdmates became fecal-culture negative by 1/97. The cow was thus defined as a chronic Salmonella fecal-shedder. In 4/97, the cow was moved to a small fenced-in pasture at a new location on which cattle had not previously grazed and on which Salmonella could not be isolated from the environment. In order to experimentally estimate the basic reproductive (transmission) rate for STC, 14 adult cows, all serologically and fecal-culture negative (2 isolation attempts) for Salmonella, were introduced into the pasture with the positive-cow. Serum, feces, and environmental samples were collected at 2-wk intervals for 3 1/2 mo. None of the naive herdmates became fecal-Salmonella positive but several showed serological evidence of exposure to STC. The chronic shedding cow became fecal culture Salmonella-negative after one month on the new pasture. The STC was not isolated from the feed, water, or environment. These findings suggest that this STC strain was not highly transmissible under these experimental conditions even though it originated from a natural field outbreak. In addition, fecal culture may be insensitive relative to serology in defining livestock Salmonella exposure.