Introduction

The human prion diseases, also known as the subacute spongiform encephalopathies, have been traditionally classified into Creutzfeldt- Jakob disease ( CJD), Gerstmann-Straussler syndrome (GSS) (also known as Gerstmann-Straussler-Scheinker disease), and kuru. Although rare, affecting about one person per million worldwide per annum, remarkable attention has been recently focused on these diseases. This is because of the unique biology of the transmissible agent or prion, and also because bovine spongiform encephalopathy (BSE), an epidemic bovine prion disease, appears to have transmitted to humans as 'new variant' CJD (vCJD), opening the possibility of a significant threat to public health through dietary exposure to infected tissues.

The transmissibility of the human diseases was demonstrated with the transmission, by intracerebral inoculation with brain homogenates into chimpanzees, of first kuru and then CJD in 1966 and 1968 respectively. (1,,2) Transmission of GSS followed in 1981. The prototypic prion disease is scrapie, a naturally occurring disease of sheep and goats, which has been recognized in Europe for over 200 years(3) and which is present in the sheep flocks of many countries. Scrapie was demonstrated to be transmissible by inoculation in 1936(4) and the recognition that kuru, and then CJD, resembled scrapie in its histopathological appearances led to the suggestion that these diseases may also be transmissible/5 Kuru reached epidemic proportions amongst the Fore linguistic group in the Eastern Highlands of Papua New Guinea and was transmitted by ritual cannibalism. Since the cessation of cannibalism in the 1950s the disease has declined but a few cases still occur as a result of the long incubation periods in this condition. The term Creutzfeldt-Jakob disease was introduced by Spielmeyer in 1922 bringing together the case reports published by Creutzfeldt and Jakob. Several of these cases would not meet modern diagnostic criteria for CJD and indeed it was not until the demonstration of transmissibility allowed diagnostic criteria to be reassessed and refined that a clear diagnostic entity developed. All these diseases share common histopathological features; the classical triad of spongiform vacuolation (affecting any part of the cerebral grey matter), astrocytic proliferation, and neuronal loss may be accompanied by the deposition of amyloid plaques.(6)

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