Prion, a type of protein molecule that can exist in an abnormal form believed to be capable of causing disease and of being infectious. Unlike such infectious agents as bacteria and viruses, the abnormal prions do not contain genetic material and cannot be readily destroyed by conventional sterilization and disinfection procedures.

The normal prion molecule is produced by brain cells and certain other cells in the body. Unlike normal prions, the abnormal form is insoluble in water and resists being broken down by common enzymes called proteases. Scientific studies indicate that the normal molecule can change into the abnormal form, either spontaneously or through contact with abnormal prions.

Prions were identified in 1982 by Stanley B. Prusiner, a United States neurologist and biochemical researcher. Prusiner was awarded the 1997 Nobel Prize for physiology or medicine for this discovery.

Prion Diseases

Most prion researchers believe abnormal prions cause several types of fatal brain diseases known as transmissible spongiform encephalopathies (TSE's). In these diseases brain cells are destroyed, leaving spongelike cavities in the brain. Some TSE's appear to be inheritable as well as infectious. In inherited TSE's, gene mutations in the body's cells cause them to produce abnormal prions.

Bovine Spongiform Encephalopathy (BSE),

a disease of cattle first identified in the United Kingdom in the mid-1980's. It is commonly called Mad Cow Disease because cattle with the disease lose coordination and move erratically. Cattle may have developed the disease from being given commercial feed made with prion-infected animal by-products.

Chronic Wasting Disease (CWD),

a disease that occurs in deer and elk in North America. Animals with the disease suffer progressive weight loss and dehydration, leading to death.

Creutzfeldt-Jakob Disease (CJD),

a rare human disease that produces such symptoms as loss of motor control and dementia. Evidence suggests that some persons may have developed a variant of CJD, known as vCJD, by eating beef from cattle with BSE.


a disease similar to CJD and first identified among New Guinea tribespeople who engaged in ritual cannibalism.


a disease of sheep. It has been known for hundreds of years. It characteristically produces a skin irritation that causes sheep with the disease to scrape against objects compulsively, rubbing the skin raw.