Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a transmissible spongiform encephalopathy and fatal neurodegenerative disease in cattle that may be passed to humans who have eaten infected flesh. BSE causes a spongiform degeneration of the brain and spinal cord. BSE has a long incubation period, of 2.5 to 5 years, usually affecting adult cattle at a peak age onset of four to five years. BSE is caused by a misfolded protein—a prion. In the United Kingdom, the country worst affected by an epidemic in 1986–1998, more than 180,000 cattle were infected and 4.4 milli...