Human prion diseases

**Definition:** Human prion diseases or transmissible spongiform encephalopathies are rare transmissible diseases affecting the central nervous system. The infectious agents are composed of an abnormal isoform of a host membrane protein called 'prion protein' (PrP). Their common features are a long duration of incubation and lesions limited to the central nervous system without inflammatory or immunologic reaction but with accumulation of an abnormal form of prion protein (PrPsc).