Some human cases of the transmissible neurodegenerative disorder Creutzfeldt-Jakob disease recently seen in Great Britain are thought to have resulted from eating beef infected with the agent of bovine spongiform encephalopathy. Reasons for and against this presumption are explained, and the question of a similar situation occurring in countries other than Britain—in particular, the United States—is discussed in terms of the existence of scrapie (in sheep) or unrecognized bovine spongiform encephalopathy (in cattle), the practice of recycling nonedible sheep and cattle tissue for animal nutrition, and precautionary measures already taken or under consideration by government agencies.
Brown P. The Risk of Bovine Spongiform Encephalopathy ('Mad Cow Disease') to Human Health. JAMA. 1997;278(12):1008-1011. doi:10.1001/jama.1997.03550120068035