Walsh & Hoyt: Bovine Spongiform Encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE), also called ""mad cow disease,"" placed prion diseases at the forefront of media attention. This disease is clinically characterized by incoordination and abnormal apprehension, progressing to death. It was first described in the 1980s by Wells and colleagues following an outbreak of bovine illness in Great Britain. The source of the disease was traced to a bovine food supplement derived from meat and bone meal prepared from dead sheep and cattle by a process known as rendering. This process had previously included prolonged, high-temperature solvent exposure with subsequent removal of the solvent using superheated steam; however, the process was changed to exclude these steps in the late 1970s, several years before the outbreak of BSE. Presumably, the initial rendering process inactivated any prions in contaminated sheep products; the altered process did not do this because the tissue was no longer exposed to prolonged, high temperatures. The altered rendering process was banned by the British government in 1988, and subsequent regulations prohibited ruminants from entering ruminant animal feed.