Study Center

A: Prions (a term derived from "proteinaceous infectious particle") are abnormal conformational forms of proteins produced by many cells in the body, especially in the central nervous system. The normal functional role of the prion proteins is not known with certainty, but there is evidence that they are involved in signal transduction. It is now believed that these abnormal forms of prions are responsible for a number of diseases known as spongiform encephalopathies that afflict both animals and humans. They are transmissible diseases characterized by behavioral and neurological disturbances as well as by accumulation of abnormal protein and sponge-like degeneration (vacuolization) in brain tissue. Until recently, many of these diseases were thought to be "slow-virus" infections; the concept of an infectious protein was highly controversial (other infectious agents are organisms or contain genetic material). But now the evidence is strong that abnormal prions can be pathogens, either through inherited abnormalities, as is the case with the familial form of Creutzfeldt-Jakob disease, or by infectious transmission, for example, scrapie, which affects sheep and goats, or kuru, a human disease once spread by cannibalistic practices in New Guinea. In 1986 an epidemic of bovine spongiform encephalopathy (BES), a prion disease affecting cattle, broke out in the United Kingdom. Afflicted animals exhibited neurological and behavior disorders including bizarre movements — hence the common name "mad cow disease." It is believed that the disease was transmitted via cattle feed derived from infected cattle and other ruminants that had not undergone proper denaturing during processing. Strong efforts were made to contain the epidemic, and it rapidly receded after peaking in 1992. However, there is evidence of a link between mad cow disease and some cases of a new variant of Creutzfeldt-Jakob disease in humans, and precautionary measures are being taken internationally to control it.