Prions are extremely small proteinaceous infectious particles that resist inactivation by the usual methods which modify nucleic acids. They are protein molecules with no nucleic acid core and are responsible for the spongiform encephalopathies which cause extensive brain damage, such as Mad Cow Disease. At least one person in 10,000 is infected and many more remain undiagnosed, especially in the UK. Symptoms are dementia, insomnia, paralysis, and wasting.
