Prions are abnormal forms of natural proteins. Stanley Prusiner (1942–) first used the term “prion” in 1982 in place of the expression “proteinaceous infectious particle” when describing an infectious agent. Prusiner was awarded the Nobel Prize in Physiology or Medicine in 1997. Current research indicates that a prion is composed of about 250 amino acids. Despite extensive and continuing investigations, no nucleic acid component has been found. Like viruses, prions are infectious agents.