Definition
Salmonellosis is the disease caused by any of more than 2000 Salmonella serotypes. In swine, only a few serotypes cause disease, usually manifested as septicemia and/or enterocolitis, sometimes by tissue localization of infection at various sites. Salmonella infections in asymptomatic swine may serve as a source of Salmonella infection to humans via contamination of pork products.
Occurrence
Infection of swine with a broad range of serotypes is common. Disease as a result of infection is relatively less common but occurs throughout the year in all major swine-raising countries. All age groups are susceptible but the disease usually occurs in weaned or growing/finishing pigs. Many other species, including people, are susceptible to salmonellosis caused by some of the Salmonella serotypes that affect swine. Contaminated pork products are not a primary source of food-borne salmonellosis outbreaks in people but efforts to reduce salmonellae in the pork food chain are a high priority for the swine industry.
Historical information
In 1886 the organism now known as Salmonella serotype choleraesuis was erroneously reported to cause hog cholera. After the viral etiology for hog cholera was identified, salmonellae were thought of as secondary pathogens. However Salmonella serotypes frequently do act as primary pathogens causing septicemia and/or enterocolitis in swine.
It has been shown that some outbreaks of salmonellosis in people are food-borne and that food products of animal origin, including pork, are sometimes are implicated as the source of these outbreaks. Species-adapted Salmonella serotypes are relatively infrequent; most serotypes are capable of infecting (though not necessarily causing disease in) multiple mammalian hosts. Both animal and human health could be improved if salmonellosis could be effectively controlled across animal production and food processing systems. Salmonella reduction programs at farm level constitute a logical step in minimizing the occurrence of outbreaks in humans. Swine industry-led national Salmonella control programs in North America and Europe are being implemented in an effort to understand what management strategies are most likely to minimize the impact of the organism on both human and animal health.
Etiology
Salmonella is now recognized as a genus with about 2000 serotypes that can be serologically clustered in groups (see serogroup examples in Table 1). Pathogenic serotypes for swine are relatively few, with most outbreaks caused by Salmonella choleraesuis orSalmonella serotype typhimurium. Serotypes that are the most common cause of disease in both people and swine include Salmonella serotypes typhimurium, enteritidis, agona andheidelberg. Salmonella choleraesuis and Salmonella serotype typhisuis are host-adapted to swine and are rarely isolated from sources other than infected swine.
Salmonellae are small, hardy, ubiquitous, Gram-negative bacilli. All contain endotoxin and are capable of elaborating a variety of other toxins. They can readily survive in many swine environments but can be inactivated by chlorine, iodine and phenol-based disinfectants.