Transmissible spongiform encephalopathy

Transmissible spongiform encephalopathies, also called prion diseases, are a group of rare, progressive, incurable and invariably fatal conditions that cause degeneration of the nervous system in humans and animals. They are caused by abnormally folded proteins called prions, which convey their misshapen structure to normal prion protein molecules through a crystallization like seeding process, progressively damaging neurons. Animal forms include scrapie in sheep, bovine spongiform encephalopathy in cattle and chronic wasting disease in deer; human forms include Creutzfeldt-Jakob disease, fatal familial insomnia, kuru and Gerstmann-Straussler-Scheinker syndrome. Unlike conventional infections caused by DNA or RNA based agents, prion diseases can arise genetically, infectiously or with no identified cause, and can spread through contaminated food, biological materials or medical procedures, though human to human transmission remains very rare.