Enteric colibacillosis is a common disease of nursing and weanling pigs caused by colonization of the small intestine by enterotoxigenic strains of Escherichia coli.
Certain strains of E coli possess fimbria or pili that allow them to adhere to or colonize the absorptive epithelial cells of the jejunum and ileum. The common antigenic types of pili associated with pathogenicity are K88, K99, 987P, and F41. Pathogenic strains produce enterotoxins that cause fluid and electrolytes to be secreted into the intestinal lumen, which results in diarrhea, dehydration, and acidosis. Infection in neonates is commonly caused by K88 and 987P strains, whereas postweaning colibacillosis is nearly always due to the K88 strain.
Profuse watery diarrhea with rapid dehydration, acidosis, and death is common. Rarely, pigs may collapse and die before diarrhea begins.
Dehydration and distention of the small intestine with yellowish, slightly mucoid fluid is characteristic. The colon contains similar fluid. The fundic portion of the gastric mucosa is often reddened. Pigs dying suddenly may have patchy cutaneous erythema. Histologically, the villi are usually of normal length and have many small bacterial rods adhered to the absorptive enterocytes.
Confirmation is based on histologic observation of villous colonization; demonstration of K88, K99, 987P, or F41 pilus antigens in intestinal scrapings by immunofluorescence or other immunologic procedures; and isolation of the organism from the small intestine. Because E coli is a common secondary agent, the possibility of involvement of other agents such as viruses or coccidia should be considered.
Therapy includes prompt treatment with antibacterials and restoration of fluid and electrolyte balance. Bacterial antibiotic sensitivity testing is helpful to identify effective medication. Prevention includes reducing predisposing factors, such as dampness and chilling; improving sanitation, such as by replacing solid or slatted concrete flooring with wire-mesh flooring; and vaccinating gestating sows with pilus-specific vaccines. Pigs lacking receptors for K88 have been shown to be resistant to disease caused by enterotoxin-positive K88-positive E coli.