Bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob Disease (CJD) are ailments in which the functioning of the brain is progressively impaired. Both diseases are associated with visually abnormal pinpoints (or plaques) in the brain, and in a changed texture of the brain tissue. The brain tissue, particularly in the cortex and cerebellum, becomes filled with large open spaces (vacuoles) and becomes spongy in texture. The "spongiform" part of BSE comes from this texture characteristic.

BSE is a disease of animals such as cattle and sheep, while CJD is associated with humans. However, the two diseases may have a common cause. The cause of BSE and CJD, and of other diseases such as scrapie, transmissible mink encephalopathy, fatal familial insomnia, and kuru, are prions. Prions are particles that are made solely of protein. Even though they lack genetic material, they are infectious.

Both BSE...