Intestinal Salmonellosis in Pigs
Enteropathogenic salmonellae cause inflammation and necrosis of the small and large intestines, resulting in diarrhea that may be accompanied by generalized sepsis. All ages are susceptible, but the disease is most common in weaned and growing-finishing pigs.
Salmonella Choleraesuis kunzendorf (S Choleraesuis) is one of the most common Salmonella species affecting pigs. It sometimes produces necrotizing enterocolitis but far more common is a septicemic disease characterized by hepatitis, pneumonia, and cerebral vasculitis. S Typhisuis infection of the intestine results in necrotizing, nonsuppurative inflammation of the mucosa and submucosa of the ileum, cecum, and colon; frequently, the mucosa is ulcerative. Usually, there is extension to regional lymph nodes and, occasionally, generalized septicemia. Sources of infection for S Choleraesuis and S Typhisuis are primarily asymptomatic carrier pigs but also may include rodents and contaminated feed and premises. (Also see Salmonellosis.)
Numerous other serotypes of salmonellae are seen in pigs, some of which have been associated with human foodborne illness. Common serotypes seen in pigs are S Typhimurium, S Derby, S Heidelberg, S Worthington, and S Infantis. These serotypes may cause mild to moderate diarrhea in swine and may be resistant to multiple drugs.
Nursing pigs may develop diarrhea but usually succumb to generalized septicemia. Weanling or growing-finishing pigs are febrile and have liquid feces that may be yellow and contain shreds of necrotic debris.
Pigs infected with S Choleraesuis have an inflamed, slightly thickened ileum and colon, usually with necrotic debris on the mucosal surface. Mesenteric lymph nodes are enlarged, edematous, and sometimes red. Mucosal ulceration may or may not be evident. A small amount of hemorrhage may be seen in acute cases. Occasionally, rectal strictures (see Rectal Strictures in Pigs) may develop. Other enteropathogenic salmonellae, except for S Typhisuis, produce lesions similar to but less severe than those of S Choleraesuis. Lesions of S Typhisuis enteritis are distinctive, typically yellow, round (button) ulcers in the colon, cecum, and less commonly the ileum.
Culture of feces or intestinal mucosa in a selective medium may yield the organism. However, salmonellae often are isolated (and more reliably) from enlarged mesenteric lymph nodes by direct streaking on a selective medium such as brilliant green agar or by inoculation of enrichment media. Histologic examination of affected intestine and liver to differentiate salmonellosis from proliferative enteritis and swine dysentery is a valuable adjunct procedure.
Live avirulent vaccines administered either intranasally or via the water are very effective for prevention of disease caused by S Choleraesuis. Avirulent vaccines may also effectively reduce levels of salmonellae in the tissues of swine at slaughter. Parenteral administration of antibacterials to acutely ill pigs and medication of the affected group via water or feed may decrease the severity of the outbreak. Neomycin and lincomycin-spectinomycin are the most often used water medications. Carbadox in the feed is often used as a preventive. Susceptibility testing of the isolated organism is useful to select an appropriate antibacterial. Thorough cleaning and disinfection of contaminated facilities and elimination of the source of the organism decrease the likelihood of repeated epidemics.