Prion diseases are a group of transmissible neurodegenerative disorders in animals. Prion-related encephalopathies are characterized by the intracerebral accumulation of an abnormal isoform of the cellular prion protein (PrPC) named scrapie prion protein (PrPSc). Prion disease is associated with a peripheral component in that the presumed causative agent, PrPSc, also accumulates in the spleen and other lymphoreticular organs.