How is a cow most likely to acquire BSE?

• A. Ingestion of the agent
• B. Either oral or aerosol transmission
• C. Fomites and vectors
• D. Addition of an infected cow into the herd

Answer: (A)

The main idea is that BSE in cattle is acquired mainly through ingesting prion-contaminated material. BSE is a prion disease, meaning it’s caused by misfolded proteins rather than a virus or bacterium. Prions are shed in nervous tissue and can persist through processing, so when cattle eat feed that contains infected tissue—historically, meat-and-bone meal made from other cattle—they can take in infectious prions. Once inside the digestive system, prions can reach the nervous system and gradually cause the brain degeneration characteristic of BSE. This ingestion route is why feed practices were the focus of control measures and bans.

Aerosol transmission and transmission by fomites or vectors aren’t considered the typical routes for BSE in cattle, and simply introducing an infected cow into a herd wouldn’t by itself reliably spread the disease, since prions are not easily transferred through casual contact or by vectors.