K99

K99, also known as the K99 antigen or F5, refers to a fimbrial adhesion associated with certain strains of enterotoxigenic Escherichia coli (ETEC). These surface structures enable the bacteria to attach to the small intestine, a key step in colonization and toxin production that can lead to diarrhea in young animals.

The K99 fimbriae are primarily implicated in neonatal diarrhea in calves and, to a lesser extent, lambs and piglets. Infection typically occurs in the first days of life and contributes to dehydration and weight loss. K99-positive ETEC strains produce enterotoxins that disrupt intestinal fluid balance, producing watery stools and illness in affected animals. The condition is a notable concern in veterinary medicine, particularly in dairy and beef operations with young stock.

Genetically, the K99 adhesin is carried on plasmids within E. coli and is used as a serotyping marker to identify K99-producing strains. Diagnosis in a veterinary setting often involves bacteriological culture with serological or molecular methods to detect the K99 antigen or the corresponding adhesin gene, alongside clinical signs and epidemiological context.

Prevention and management focus on improving colostrum intake and overall calf health, along with farm hygiene. Vaccination of pregnant dams to promote passive immunity in colostrum is one strategy, complemented by stringent sanitation, proper colostrum management, and prompt supportive care for affected animals. Antibiotics may be used under veterinary guidance to treat secondary infections or severe dehydration, but are not a standalone substitute for rehydration and preventive measures.