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Swine are often asymptomatic carriers of Salmonella spp. Interventions are needed to limit Salmonella colonization of swine to enhance food safety. An attenuated Salmonella enterica serovar Typhimurium mutant strain (BBS 202) was tested in swine to determine whether vaccination could provide protection against wild-type S. Typhimurium challenge. Two groups of piglets (n=14/group) received an intranasal inoculation of BBS 202 or a PBS placebo at 6-weeks of age with a booster 2-weeks later. At 11-weeks of age, all pigs were challenged with the parental, wild-type S. Typhimurium by intranasal inoculation. Average swine rectal temperature (fever) was significantly decreased in BBS 202-vaccinated pigs at days 1 and 2 post-challenge with virulent S. Typhimurium compared to mock-vaccinated pigs. Fecal shedding of wild-type S. Typhimurium was significantly reduced at 2-days post-challenge in BBS 202-vaccinated pigs compared to mock-vaccinated pigs. Colonization of tissues within the gastrointestinal tract by wild-type S. Typhimurium was reduced in BBS 202-vaccinated pigs; a significant decrease in S. Typhimurium colonization of the ileal Peyer’s patch region and ileocecal lymph nodes at 7-days post-challenge was observed. Serological analysis using the IDEXX HerdChek Swine Salmonella Test Kit indicated that all pigs were negative for antibodies to LPS derived from Salmonella serogroups B, C1, and D prior to challenge with wild-type S. Typhimurium. Thus, although vaccinated pigs had received two doses of BBS 202, antibodies from these pigs were not reactive to the LPS antigen in the ELISA test. However, sera from 85% of vaccinated and 78% of mock-vaccinated pigs were positive in the ELISA assay at day-7 post-challenge with wild-type S. Typhimurium. These preliminary results indicate that vaccination of swine with BBS 202 confers protection against challenge with virulent S. Typhimurium by reducing disease severity, pathogen fecal shedding, and gastrointestinal colonization but does not interfere with herd level monitoring for Salmonella spp., thereby allowing for differentiation between pigs naturally infected with Salmonella spp. and BBS 202-vaccinated swine. Introduction An estimated 1 million cases of foodborne illness are attributed to nontyphoidal Salmonella spp. each year in the U.S. at a predicted cost of $2.3 billion (Scallan, 2011; Frenzen, 1999). Nontyphoidal Salmonella spp. are a leading cause of hospitalization (35%) and death (28%), in the U.S., due to foodborne disease (Scallan, 2011). There are greater than 2,400 Salmonella serovars that are ubiquitous in the environment and many can colonize food producing animals and poultry as well as wild animals and birds without causing overt disease. In the U.S., ~100,000 cases of pork-associated, human salmonellosis occur each year with a social cost of $81 million annually (Miller, 2005). Swine 2006, the most recent study from the USDA’s National Animal Health Monitoring System, reported that 52.6% of swine production sites (representing 94% of the U.S. swine inventory) were positive for Salmonella spp. Swine that are Salmonella carriers are a food safety risk for consumers of pork, an animal health risk to non-colonized/uninfected pigs, and an environmental risk due to fecal shedding of the pathogen into swine manure that is used as a soil amendment. Interventions are needed to limit the colonization of swine with Salmonella spp. and reduce the risks to public health, animal health and the environment. We investigated an attenuated Salmonella enterica serovar Typhimurium strain to determine whether administration of the potential vaccine strain would 1) protect swine against virulent S. Typhimurium challenge while 2) allowing the differentiation of infected and vaccinated animals (DIVA) using the IDEXX HerdChek Swine Salmonella Test Kit. Our results indicate that BBS 202-vaccinated pigs have reduced disease severity, pathogen fecal shedding, and gastrointestinal colonization due to virulent S. Typhimurium challenge, but swine vaccination did not interfere with the herd level monitoring system for Salmonella spp.

international conference on the epidemiology and control of biological, chemical and physical hazards in pigs and pork

Serological Response of Swine to an Attenuated Salmonella enterica serovar Typhimurium Strain that Reduces Gastrointestinal Colonization, Fecal Shedding and Disease due to Virulent Salmonella Typhimurium