A prion, short for "proteinaceous infectious articles," is a protein capable of causing both inheritable and communicable disease by inducing benign proteins to change their shape. This shape change renders the protein infectious. When the notion of prions was first suggested in the 1970s by Stanley Prusiner, a neurologist at the University of California at San Francisco, it was heretical. Dogma held that the conveyers of transmissible diseases required genetic material, composed of nucleic acid (DNA or RNA), in order to establish an infection in a host. Time and the accumulation of experimental evidence proved Prusiner correct. For his discovery of prions and the elucidation of their infectious mechanism, Prusiner received the 1997 Nobel Prize in medicine.

The known prion diseases, all fatal, are known as spongiform encephalopathies. They frequently cause the brain to become riddled with holes, and rod-shaped particles clumped together in large arrays are evident. The...