What Is a Prion?

Unlike viruses or bacteria, prions contain no DNA or RNA — they are simply abnormally shaped versions of a normal brain protein called PrP. When a misfolded prion contacts a healthy PrP molecule, it induces the healthy protein to refold into the same abnormal shape, creating a chain reaction. The accumulating misfolded proteins form insoluble clumps that destroy brain tissue, leaving it riddled with microscopic holes — a "spongy" appearance. Prion diseases include Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy (mad cow disease) in cattle, and chronic wasting disease in deer.