Transmissible spongiform encephalopathy

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are a group of rare, progressive, incurable, and invariably fatal conditions that cause degeneration of the nervous system in humans and other animals, such as cattle and sheep. Prion diseases are caused by abnormally shaped proteins called prions, an idea once considered radical, but now well supported by evidence.