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vCJD: the epidemic that never was

Editor—Venter's article on new variant Creutzfeldt-Jakob disease (vCJD) is intended to stimulate debate, which we hope will be better informed than the article itself.1 
 
Is variant Creutzfeldt-Jakob disease a new disease? Venters places great emphasis on Creutzfeldt's case, but this patient did not have Creutzfeldt-Jakob disease. The illness was characterised by gait disturbance, a relapsing and remitting course, nystagmus, and status epilepticus. These are not the clinical features of variant Creutzfeldt-Jakob disease and, crucially, the neuropathological appearances were “not characterisitic of Creutzfeldt-Jakob disease.”2 
 
In 1996 confidence in the novelty of variant Creutzfeldt-Jakob disease was based largely on the identification of a neuropathological phenotype that was distinct from that experienced in the United Kingdom from 1970. Since then archival tissues have been reviewed in many countries and no past cases with a similar neuropathological pattern have been found.3 Retrospective epidemiological surveys in England and Wales have not identified any missed cases of variant Creutzfeldt-Jakob disease from 1979-96.4 Current evidence strongly supports the hypothesis that variant Creutzfeldt-Jakob disease is indeed a new disease. 
 
Was variant Creutzfeldt-Jakob disease identified solely because of improved surveillance? There was a doubling in the annual death rates for sporadic Creutzfeldt-Jakob disease in the United Kingdom between the 1980s and the 1990s, but similar increases in the apparent death rates for sporadic Creutzfeldt-Jakob disease had occurred in other European countries.5 These countries have been subject to similar potential improvements in case identification, but variant Creutzfeldt-Jakob disease remains a disease occurring predominantly in the United Kingdom, despite significant numbers of young suspect cases being investigated in each country (figure). 
 
Venters argues correctly that the curve for the epidemic of variant Creutzfeldt-Jakob disease does not parallel the number of cattle with bovine spongiform encephalopathy (BSE) between 1983 and 1988. However, human exposure to the BSE agent almost certainly extended to 1996 and depended on a range of variables not addressed by his model. These include the species barrier between cattle and humans, the numbers of cattle in the final year of the incubation period, the load of bovine central nervous tissue entering the human food chain, the efficiency of legislative measures, and temporal changes in food production. Extrapolation from conventional foodborne epidemics to epidemics of variant Creutzfeldt-Jakob disease and BSE is clearly too simplistic. 
 
A wealth of laboratory evidence supports the hypothesis that the BSE agent is the cause of variant Creutzfeldt-Jakob disease.6 Venters states correctly that there is no direct evidence that the BSE prion is infectious to humans, but obtaining such evidence would be difficult to justify ethically as this would involve inoculating humans with the agent. A judgment on the link between BSE and variant Creutzfeldt-Jakob disease inevitably depends on an assessment of a range of clinical, pathological, epidemiological and laboratory based evidence. There is now overwhelming evidence that BSE is the cause of variant Creutzfeldt-Jakob disease, although there remain uncertainties about the future number of cases and the mechanism of transmission of BSE to humans.