Technical Abstract: Bovine spongiform encephalopathy (BSE), also referred to as “mad cow disease” is a chronic, non-febrile, neuro-degenerative disease affecting the central nervous system. The transmissible spongiform encephalopathies (TSEs) of domestic animals, of which BSE is a member includes scrapie of sheep and goats, chronic wasting disease (CWD) of elk, moose, mule and white tailed deer, feline spongiform encephalopathy and transmissible mink encephalopathy. The central factor in BSE pathogenesis is the accumulation in the CNS of a misfolded version of the normal prion protein. The key component of BSE pathogenesis which helps explain the worldwide decline in BSE cases is the absence of horizontal (contact) transmission. This characteristic of BSE pathogenesis is in contrast to the efficient horizontal transmission of CWD and the less efficient but clearly horizontally transmitted scrapie of sheep.