Between 1986 and 1989, a disease swept through British cattle herds. The disease came to be known as the Mad-cow disease. Scientist began to suspect that this was somehow related to some human illness. A California neurologist, said both humans and animals were suffering from a mutated prion. When defective prions are transmitted from an infected host to a new host, they convert any normal prions they come across into copies of themselves. So it is possible for a mutated prion to be transmitted from a cow to a person by eating beef. Dr. Stanley B. Prusiner received a Nobel prize for his work with prion. (thetvdb.com)