Mad cow disease, or bovine spongioform encephalopathy (BSE), is a prion disease. Prion diseases are a group of rare communicable diseases affecting both humans and animals. They are progressive degenerative diseases of the brain, characterized by the spongy texture of the brain (or holes in the brain) and dementia. Prion diseases have a long incubation period and are invariably fatal. The cause is infectious abnormal prion proteins in the brain and spinal cord, which are folded and distorted, and which can contaminate normal prion proteins, causing increasing damage to the brain.
Besides BSE, prion diseases in animals include Chronic Wasting Disease (in deer and elk), Scrapie (in sheep and goats) and similar diseases in mink, felines and ungulates. Human prion diseases include Creutzfeldt-Jakob Disease(CJD) and a variant of CJD, Gerstmann-Straussler-Jakob Syndrome, Kuru and Fatal Familial Insomnia. The disease can occur spontaneously for unknown reasons, it can be inherited (fatal familial insomnia) and it can be transmitted through the food chain when the brain or spinal tissue of an animal with mad cow disease is eaten by humans or by another animal (kuru.)
Mad cow disease was first discovered in Britain in 1986 and it killed approximately 150 people and 184,000 cattle. It was caused by widespread use of meat and bonemeal cattle feed made from scrapie-infected sheep. People who died from the disease were probably exposed to it by eating processed beef contaminated with BSE. Since then the U. S., Europe and Canada have banned feeds produced with the meat and nerve tissue of animals, significantly reducing the transmission of BSE.
How likely is it that any of us will contract prion disease from meat? The infectious protein isn’t found in muscle, just in brain and spinal cord tissue, so it’s likely that eating steaks, roasts and so forth is safe. Processed meat is slightly riskier as it is made from many varieties of meat, including tissue stripped from the spine by the processing machines.
Current laws and meat processing procedures are designed to prevent the spread of BSE to animals or humans. So the question is whether you trust that everyone in the meat processing industry scrupulously follows the safest procedures. It’s highly unlikely, statistically speaking, that any one of us will get prion disease from eating contaminated meat. However, if you don’t want to be the first person in the U.S. to develop BSE from meat, the solution is to not eat beef, goat, sheep, elk or deer, and especially to not eat processed meat.
Journal of the American Medical Association: Risk of transmission of bovine spongiform encephalopathy to humans in the United States: report of the Council on Scientific Affairs
The Family That Couldn't Sleep: A Medical Mystery. Max, D. T. 2007