Ever since Gajdusek implicated a “slow virus” in the transmission of Kuru, the oral route of “infection” of spongiform encephalopathies has attracted considerable interest. Transmission studies in transmissible spongiform encephalopathies (TSEs) have currently become an even more important area of study due to the possible transmission of bovine spongiform encephalopathy (BSE) to humans resulting in “new variant” Creutzfeldt-Jakob disease (vCJD). Prusiner’s hypothesis that TSEs are caused by small proteinaceous infectious particles “prions” took considerable time to gain widespread recognition among the scientific establishment. The importance of these discoveries was vindicated by awards of Nobel prizes to Gajdusek and more recently to Prusiner. Two forms of prion proteins are recognised—normal host encoded cellular prion protein (PrP) and its pathological malfolded isoform (PrP)—which accumulate in the brain in TSEs including vCJD. PrP is a copper binding glycoprotein attached to the plasma membrane through a glycosyl-phosphatidyl-inositol anchor. 2 Although both isoforms are identical in amino acid sequence, they diVer in their secondary structure: PrP is high in â sheet content in contrast with the predominantly á helical structure of PrP. Partial resistance to proteolytic degradation, detergent insolubility, and slower turnover rate also characterise the pathological isoform.