[Epidemiology of human prion diseases]

Prions(proteinaceous infectious particles) are responsible to subacute spongiform encephalopathies(SSE) in man and animals. Recent outbreak of bovine SSE(BSE), or mad cow disease in UK provoked concerns on its possible human hazards. A statement of the British Government in March 1996 upset the world, which was based on 10 cases of "new variant" form of Creutzfelds-Jakob disease(CJD). Prion diseases in animals are often epizootic and may be spread to different species through various routes including ingestion of contaminated meats. It is possible that mad cow disease cause a CJD-like malady in man through a dietary route. Human SSE include; 1) Classical CJD, which represents over 95% of the cases with SSE, dispersely sporadic in occurrence in 1 per million a year, with monotonously rising incidence rates with age, of which the origin of the prion is totally unknown. 2) Gerstmann-Sträusseler Scheinker's disease which is inherited dominantly due to various genetic variants of the prion. 3) Transmitted cases of CJD occurring due to the prion introduced through contaminated objects either directly to the brain or its coverings, or indirectly to the brain through peripheral organs. 4) Kuru occurring among the Fore people in Papua New Guinea, probably due to the prion spread by a dietary route in cannibalism. New variant CJD(vCJD) now totals 14 cases all observed in UK and is different from all of four, is encountered in a dispersely sporadic manner, is far younger at onset than classical cases, showing kuru-plaques. Prions from vCJD have physical-chemical properties similar to those the BSE. Countermeasures in Japan against human hazards of BSE include, 1) agent controls by means of quarantine and 2) host controls. Sofar no vCJD-like case is observed in Japan. An emergent surveillance for CJD was introduced by the Ministry of Health and Welfare in July 1996. It obtained a total of 2,637 answers form 4,027 departments of neurology, psychiatry, etc throughout the country and identified 766 cases including 51 familial cases, but no case with vCJD.