Which statement is true about E. coli O157:H7 in cattle?

• A. It is very pathogenic in cattle
• B. It is not very pathogenic in cattle
• C. It is harmless to cattle
• D. It is more pathogenic than other strains

Answer: (B)

A pathogen can be carried by a reservoir host with little or no disease, yet cause illness in another species. In cattle, E. coli O157:H7 mainly colonizes the gut and is shed in feces, but cattle typically do not develop significant illness from this strain. That makes it not very pathogenic in cattle—the animals are largely asymptomatic carriers. The public health concern comes from cattle acting as a reservoir, allowing contamination of beef or dairy products that can cause severe disease in humans who consume or handle them. The other statements suggest high pathogenicity in cattle, harmlessness, or greater virulence than other strains, which doesn’t fit how this organism behaves in its cattle host.