One of the transmissible spongiform encephalopathies (TSEs) of animals alleged to be caused by a prion protein. Currently, the ultimate reservoir is thought to be sheep and goats; transmission is by direct ingestion or contact with brain tissue. The transmissible form in sheep is denoted by PrPSc (S for sheep) and appears to have been transmitted horizontally from sheep to cows (BSE) to humans (nvCJD).