In 1997, American biology professor Stanley B. Prusiner won the Nobel Prize for medicine for discovering “prions,” described as “an entirely new genre of disease-causing agents.” The name means “proteinaceous infectious particle.” Prions cause brain diseases such as BSE (Bovine Spongiform Encephalopathy or “mad cow disease”); the human variant Creutzfeldt–Jakob disease; kuru among some peoples in New Guinea; and scrapie in sheep and goats. Prions are too small to be seen with normal microscopy. They are self-replicating, but contain no nucleic acid. Prions are highly resistant to destruction or denaturation by common chemical and physical agents such as disinfectants, formalin, heat, UV or ionizing radiation. Inceration of infected tissues requires a temperature never below 900ºF for four hours.«