HERD HEALTH
PIH-131
PURDUE UNIVERSITY COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
pork
industry handbook
Salmonella choleraesuis in Swine
Author:
Kent J. Schwartz, Iowa State University
Reviewers:
Larry Ritter, Mitchell, South Dakota
David Striegel, Sac City, Iowa
Salmonellosis, the disease that may result from Salmonella infection, continues to have a significant economic impact on the national swineherd. Between 1975 and 1995, S. choleraesuis was one of the most common organisms isolated from cases of swine pneumonia and septicemia. It also was the most prevalent serotype (>90% of isolates) of all Salmonella isolated from diseased swine. In 1991, it was estimated that the disease caused by S. choleraesuis cost pork producers in the United States more than $100 million annually due to death losses, medication costs, and poor production efficiency of survivors. Since the mid-1990’s, the prevalence of S. choleraesuis-associated disease has moderated. Currently, serotypes of Salmonella other than S. choleraesuis have increased in frequency and presently account for over 50% of the serotypes isolated from diseased swine.

In addition, concerns over Salmonella-contaminated pork products as a human health hazard add to processing and monitoring costs of pork products and may impact overall product demand. All Salmonellaspp. are considered pathogenic for humans but Salmonella choleraesuis is rarely isolated from pork products.

Salmonellosis in swine occurs as either of two general clinical disease entities. Enterocolitis (diarrhea) may be caused by a broad range of Salmonella serotypes, including S. choleraesuis, but S. typhimurium is more common. Septicemia (affecting multiple organ systems) is due to Salmonella choleraesuis. Salmonella are notoriously diverse. This publication discusses only S. choleraesuisas a cause of disease in swine.

History
Salmonella was among the first bacteria discovered, and it was first observed microscopically in 1880 in tissues from humans dying from typhoid fever. The causative organism,
Salmonella typhi, was first isolated in 1884. The first isolation from animals was Salmonella choleraesuis, which was isolated in 1885 by Salmon and Smith from pigs that had died of hog cholera. Salmonella choleraesuis was considered to be the cause of hog cholera until 1904 when a virus was proven to be the etiologic agent.

Etiology
Salmonella are a genus of Gram-negative bacteria that contains more than 2,000 serovars, sometimes referred to as species or serotypes. These organisms are very common in animal populations and feces, residing in the intestinal tracts and feces of both warm- and cold-blooded animals. Salmonella are quite hardy and are able to survive for months in cool organic substrates in either aerobic or anaerobic environments. Since some Salmonella survive within animal cells (phagocytes), intestinal tracts, or feces for extended periods of time, the organism is unlikely to be eradicated. Fortunately, Salmonella are quite sensitive to disinfection with most common disinfectants, but only after thorough cleaning and removal of organic debris.

Salmonella choleraesuis causes the majority of cases of salmonellosis in pigs. Salmonella typhimurium, the other major cause of porcine salmonellosis in the United States, accounts for 30% of swine outbreaks. Infections of pigs with other Salmonella serovars frequently occur but are only occasionally causes of disease outbreaks.

Zoonotic Potential
Salmonella choleraesuisls considered to be host-adapted to pigs, meaning that infection and disease due to this organism is limited almost exclusively to pigs, and persistent infections can occur in pigs without signs of disease. Although infection of other species of animals (and humans) is rare, S. choleraesuis
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