A family of diseases sharing some common characteristics, including a prolonged incubation period ranging from a few months to years and progressively debilitating neurological illnesses, which are always fatal. Examples of other TSEs include scrapie (sheep and goats), chronic wasting disease (deer and elk), feline spongiform encephalopathy (cats), kuru (humans), Creutzfeldt-Jakob Disease (humans), and variant Creutzfeldt-Jakob Disease (humans).