Alpers disease

The possible consequences of the exposure of large populations to bovine spongiform encephalopathy (BSE) raise major public health concern. Among the studies which have been conducted since the identification of new variant Creutzfeldt-Jakob disease in 1996, some have contributed to this concern while others provided reassuring results.

To date, only 38 cases of new variant Greutzfeldt Jakob disease have been reported by the national surveillance unit in Edinburgh and, except one in France, no case has been identified in any other European country. The results of Aylin et al add to the reassuring evidence. They examined mortality from Creutzfeldt-Jakob disease and other dementias among groups with potentially high exposure to bovine spongiform encephalopathy. Analysis did not show any increase in mortality during 1979-96. In particular, mortality from dementia was stable over the study period, suggesting that atypical Creutzfeldt-Jakob disease did not constitute an important proportion of the dementia category.

The absence of any increasing trend in population groups with high exposure to bovine spongiform encephalopathy increases optimism about the size of a putative future epidemic. However, these results must be interpreted with caution because predictions based on currently available data are affected by the length of the incubation period of the disease.

The European Union collaborative study of Creutzfeldt-Jakob disease showed that the peak incidence of classic sporadic disease occurred in the 70-79 year age group and that the disease was extremely rare under the age of 40 years. This distribution of age at disease onset suggests a slow, endogenous or acquired, neurodegenerative process associated with accumulation of the pathological prion protein in the brain. In iatrogenic Creutzfeldt-Jakob disease the exact date or length of exposure to infected materials can be defined, allowing the length of the incubation period to be estimated. Reports indicate that the incubation period may vary from 2 years to more than 30 years. In Kuru, another transmissible spongiform encephalopathy which was mainly acquired by oral route, the incubation period is variable and can exceed 20 years.

The incidence of bovine spongiform encephalopathy in cattle increased rapidly from the early 1980s to 1992-3, then decreased. If the incubation period of new variant Creutzfeldt-Jakob disease is short, then those who have developed the disease since 1995 have been infected when the level of exposure was high. If the incubation is 15 years or more, then these people were infected when the level of exposure was low. The results of Aylin et al support an optimistic scenario about the size of a future epidemic of new variant Creutzfeldt-Jakob disease if the incubation is short, but with a longer incubation less optimistic prospects cannot be excluded. This uncertainty re-emphasises the need to continue epidemiological surveillance of Creutzfeldt-Jakob disease in Europe.

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[2] Hill AF, Zeidler M, Ironside JW, Collinge J. Diagnosis of a new variant Creutzfeldt-Jakob disease by tonsil biopsy. Lancet 1997;349:99-100.

[3] Hilton AF, Fathers E, Edwards P, Ironside JW, Zajick J. Prion immunoreactivity in appendix before clinical onset of variant Creutzteldt-Jakob disease. Lancet 1998;352:703-4.

[4] Cousens SN, Vynnycky E, Zeidler M, Will RG, Smith PG. Predicting the CJD epidemic in humans. Nature 1997;385:197-200.

[5] Will RG, Alperovitch A, Poser S, Pocchiari M, Hofman A, Mitrova E, et al. Descriptive epidemiology of Creutzfeldt-Jakob disease in six European countries, 1993-1995. Annals of Neurology 1998;43:763-7.

[6] De Silva R, Esmonde T Iatrogenic transmission of Creutzfeldt-Jakob disease. CNS Drugs 1992;2:96-101.

[7] Prusiner SB, Gadjusek DC, Alpers MP. Kuru with incubation periods exceeding two decades. Ann Neurol 1982; 12:1-9.

Institut National de la Sante et de la Recherche Medicale, Research Unit 360 Epidemiologie des Maladies Neurologiques, Hopital La Salpetriere, 75651 Paris, Cedex 13, France

Annick Alperovitch, head, unit 360

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