#04-100

Complete

Date Full Report Received

10/10/2006

Date Abstract Report Received

07/21/2008

Investigation

Institution:
Primary Investigator:
Co-Investigators: James McKean, Marcos Rostagno

This research project was conducted with the objective of determining if the Salmonella prevalence at the end of the finishing production stage correctly represents the Salmonella status of a lot, as a high or low Salmonella prevalence lot. An important discrepancy between bacteriologic and serologic prevalence estimates was found. Although all lots of pigs studies were persistently negative through bacteriologic testing, they were all serologically positive at slaughter. How can all the studied lots be bacteriologically negative for Salmonella during the entire growing-finishing production stage (i.e., over a period of 17 weeks), but be serologically positive at slaughter? This question leads to re-thinking the complex ecology and epidemiology of Salmonella in swine herds, and a consequent formulation of fundamental questions: How well does serology represent the real microbial food safety risk at the time of slaughter? How long do infected pigs carry and shed Salmonella? How long does the serologic response to a Salmonella infection last in pigs? Although the number of published studies on the epidemiology of Salmonella in subclinically infected pig herds has tremendously increased over the past decade, longitudinal studies following both the bacteriologic and serologic statuses of pigs are still necessary to understand their dynamic and inter-relationship. Moreover, to design effective pre-harvest monitoring and control programs, an understanding of the transmission of Salmonella, taking into account a number of variables (e.g., serotype, age of infection, infectious dose, route of infection, diet configuration, environmental exposures, etc.) on farms, is essential.
This research generated valuable information, besides of raising critical questions that need to be answered in order to advance our understanding of the ecology and epidemiology of Salmonella in swine populations.