Trends in Salmonella shedding by U.S. market hogs, swine 2000.

USDA’s National Animal Health Monitoring System’s (NAHMS) conducted a study of the health and management of swine as part of the Swine ‘95 study and Swine 2000 study. The studies were conducted in the top swine states in the U.S. A subset of participating farms allowed collection of fecal samples (50 samples per farm) from pens containing late finishers. The same methodology and laboratory was used in both studies so comparison of results provides a measure of change in on-farm Salmonella status between 1995 and 2000. Samples were tested for Salmonella and questionnaires were used to obtain management data regarding feed management, environmental conditions, vaccination policies, and other factors. The percent of farms with at least one positive sample was 38% in 1995 and 34% in 2000. The percent of samples positive was 6% in 1995 and 2000. The percent of pens positive was 17% in 1995 and 16% in 2000. In contrast to trends in slaughter HACCP Salmonella samples, the similarity in on-farm Salmonella status suggests that on-farm Salmonella intervention has yet to be initiated on a wide scale by producers and that on-farm Salmonella status is not directly related to slaughter Salmonella status

Mechanisms of host-agent interactions in subclinical salmonella infection in pig herds

Salmonella spp. are ubiquitous in nature and have been recovered from nearly all vertebrates (Taylor and McCoy, 1969) and there is little dispute that Salmonella is an intestinal pathogen (D\u27Aoust, 1991; Hsu, 1989). Typically, the organism is thought to pass through the stomach after oral exposure, enter into the intestine, replicate intraluminally, pass through the glycocalyx, undergo endocytosis through the cell cytoplasm, then exocytosis through the basement membrane (Hale and Formal, 1988). Malabsorption and/or the release of prostaglandins may play a role in the manifestation of diarrhea (Gianella et al., 1973). Other factors that may influence fluid loss include the presence of an enterotoxin or cytotoxin/hemolysin (Prasada et al., 1990; Libby et al., 1990; Reitmeyer, 1986)

Prevalence of Salmonella in Swine and Pork: A Farm to Consumer Study

Fecal, tissue, and environmental cultures and serological tests were performed on 100 swine on a multi–site farrow to finish production facility. Salmonella of 10 types were identified in the swine herd and environment but none were recovered from rodents or flies caught in the production units. At slaughter, 52% (24 of 46) of swine were serologically positive for Salmonella antibodies, while 9% (4 of 46) were positive by culture. Although clinical salmonellosis was not detected in the study herd, multiple serotypes of Salmonella were causing endemic infections in the study herd

The association between herd characteristics and salmonella prevalence in slaughter age pigs

Many factors have the potential to result in exposure of pigs to Salmonella and/or to increase the potential shedding at the time of slaughter. Observation of selected production systems has suggested that control of Salmonella may not occur using common disease management strategies, such as batch pig flow, as do many other diseases.\u27 A rational approach to Salmonella reduction would be to rank risk factors, to aid in selecting. We designed this study to assess risk factors of Salmonella status at slaughter

Long Term Survival and Infectivity of Salmonella Choleraesuis

It is believed that Salmonella cho leraesuis, the host-adapted serotype of swine, does not survive well outside the host. Pigs were infected with S. Choleraesuis and feces was collected and pooled on days 2, 4, 7 and 10 post inoculation (PI). Feces was stored in a wet and a dry form and survival was measured over 13 months. Salmonella Choleraesuis was recovered from wet feces through 3 months of storage. In a desiccated (dry) form, S. Choleraesuis was recovered from at least 13 months. Direct PCR analysis did not detect S. Choleraesuis subsequent to culture. We also examined the infectivity of S. Choleraesu is resident in dry feces. Six or 13 week old pigs were inoculated with dry feces that had been stored either 2 months or 4 months, respectively. Pigs were inoculated either intranasally or by mixing dry feces with feed. Although clinical signs were mild, S. Choleraesuis was widely disseminated among the tissues of all the pigs inoculated. This study demonstrates that S. Choleraesuis remains viab le and infective in the environment. Contaminated fecal matter can serve as a reservoir for S. Choleraesuis

Farm-level Risk Factor Assessment for Infection with Salmonella spp.

We are focusing on the factors that predispose to Salmonella spp. infection in commercial pig production systems. Our current project aims to accomplish two primary goals. First, we will define the herd-level and pig-level prevalence for Salmonella infection. Second, we will quantify the farm-level risk factors for Salmonella herd- and pig-level prevalence. The determination of Salmonella infection is species and serotype specific. Twenty-five pigs will be sampled on the farm and 15 at slaughter from each of 70 herds that participate in an ongoing slaughter monitoring project (PigMON). Risks will be assessed by a survey of farms at the time of the slaughter inspection

Control of Salmonella Virulence in the Natural Host

The long term goal of this research is to understand the mechanisms that govern Salmonella virulence in the natural host. Much of the genetic and pathogenesis studies have focused on using the murine model of salmonellosis. Although the results from using the model have been useful, there have been several cases where mutants of Salmonella not showing virulence in mice have been virulent in the natural host and visa versa. Therefore, virulence may be mediated by the host to some degree. We have chosen Salmonella choleraesuis which is host-adapted to swine, to study particular genes that may be crucial in causing disease. Specifically, we have begun a project to evaluate several mutants of Salmonella choleraesuis and test them for virulence. We will use strains containing separately or in pairs the following mutations: sly, rpoS, and spvR

The association of antimicrobial resistance patterns and reported usage of antimicrobials in commercial growing pig production

The relationship between into microbial use and the development of resistance to antimicrobials has been demonstrated through both external models and has been observed clinically. However, the strength of this relationship in practical production systems has not been clearly quantified. We designed this study to examine the strength of the relationship between use of antimicrobials and the occurrence of antimicrobial resistence among Salmonella spp. collected from the same groups of growing pig

Salmonella prevalence and antimicrobial resistance in swine from 5 US states from 2003 to 2005

The Collaboration in Animal Health and Food Safety Epidemiology (CAHFSE), a USDA joint program of ARS, APHIS, and FSIS was established to track food borne pathogens and monitor animal health issues. Fecal samples (n=9020) were collected and cultured for Salmonella from pens of pigs near slaughter weight (generally~ 22 weeks old) from swine farms in five U.S. states. A prevalence of 8.0, 10.1, and 8.5% was observed in 2003, 2004, and 2005, respectively The top 10 serotypes accounted for 94% of the total Salmonella isolates with S. Derby (45%), S. Typhimurium var. 5- (15%), and S Heidelberg (9%) comprising the top three serotypes each year. Salmonella Give was found in 8% of samples in 2003, 3% of samples m 2004, but was not found in the top 10% of ISolates m 2005. The percentage of Salmonella isolates that were susceptible to all of the 16 antimicrobials tested increased from 6% in 2003 to 15% in 2005. At the same time, the percentage of isolates resistant to 10 or more antimicrobials increased from 1% to 15%. The increase in multiple drug resistance was coincident with an increase in the percentage of S. Derby isolates. Overall, frequency of resistance to individual antimicrobials was relatively stable from 2003 to 2005 and observed differences were related to changes in serotypes over time, which highlights the importance of reporting resistance data by individual serotype. CAHFSE provides a mechanism to monitor changes in serotypes of Salmonella as well as antimicrobial resistance patterns over time