Which species transmits and poses the greatest risk for zoonotic E. coli O157:H7?

• A. Cattle
• B. Pigs
• C. Sheep
• D. Horses

Answer: (A)

Cattle are the primary reservoir for zoonotic E. coli O157:H7. This bacterium colonizes the bovine intestinal tract and is shed in feces without causing illness in the animals, leading to contamination of hides, carcasses, farm environments, and dairy products. Because ground beef and other animal products can become contaminated during processing, and because people may come into contact with cattle or their environment at farms, fairs, or petting zoos, cattle represent the biggest source of human exposure. While other animals can carry various E. coli strains and occasional O157:H7, the prevalence and direct risk to people from cattle are the greatest, making cattle the species most associated with transmission and zoonotic risk of this pathogen.