The family of fatal brain disorders caused by prions, including mad cow disease in cattle, Creutzfeldt-Jakob disease and kuru in people, and scrapie in sheep. They creep forward silently for years or even decades before symptoms appear, then progress rapidly with loss of coordination and cognitive decline. Because the infectious protein survives cooking, rendering, and standard disinfection, control depends on removing high-risk tissues from the food chain, banning ruminant-derived feed for ruminants, and surveillance of cattle populations. No treatment exists, so prevention is the entire strategy.