Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a fatal neurodegenerative disease in cattle which causes a spongy degeneration of the brain and spinal cord. The disease has a long incubation period, lasting from about two-and-a-half to eight years, and usually affects adult cattle at a peak age onset of four to five years; all breeds are equally susceptible. In the United Kingdom, more than 180,000 cattle have been affected and 4.4 million slaughtered in an attempt to stem the spread of the disease. The United Kingdom has been affected by the spread of mad cow more than any other country.
Mad cow can also be transmitted to humans by the consumption of food contaminated with the brain, spinal cord, or digestive tract of infected carcasses. Though the infectious agents are most highly-concentrated in nervous tissue, they can also be found in virtually all of the body’s tissue and in blood. There is also a human-specific variant known as Creutzfeldt-Jakob disease which, by October 2009, claimed the lives of 166 people in the United Kingdom and forty-four people elsewhere.