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If variant Creutzfeldt-Jakob disease (vCJD) is caused by bovine spongiform encephalopathy (BSE) it must be a new disease, as human exposure to the BSE agent is unlikely to have happened much before 1983.1 The study by Hillier et al (this issue, pp 304–309)2 adds significantly to the evidence supporting the hypothesis that vCJD really is a new disease, with the caveat that the study unavoidably had incomplete follow up data. No previously unrecognised cases of vCJD were found in a systematic retrospective study in Wales, which included review and restaining of available neuropathological tissue. A similar study based on death certificates in England and Wales between 1979 and 1996 also failed to identify missed cases of vCJD3 and no case with a similar neuropathological phenotype to vCJD has been identified in any country despite extensive review of archival neuropathology tissues. Although there are still doubters,4 informed opinion supports the view that vCJD really is a new disease.5,6 It is important to recognise that the availability of stored brain samples was critical to the identification of vCJD7 and to the study of Hillier et al2. Defending medical activities deemed by some to be ethically controversial is essential both for research and informed clinical practice.8
Although the clinical features of the first three cases of vCJD were judged to be “well within the recognised diagnostic spectrum for CJD”,9 the neurological phenotype of vCJD is relatively distinct from sporadic CJD and also fairly consistent between cases.10 The implication is that it is likely that cases of vCJD are being identified in life by neurologists and, assuming notification to the surveillance system, that the figures on numbers of cases of vCJD are accurate. There is a separate surveillance system for vCJD in children,11 which has led to the identification of six cases of vCJD where the patient's age was less than 16 years at onset of symptoms. The diagnosis of vCJD has been confirmed in a patient aged 74 years,12 significantly extending the age range and raising questions about the efficiency of surveillance in elderly people. Accuracy of data on the numbers of cases of vCJD is critical to public health planning and to both short term and long range forecasts of the future of the vCJD epidemic.
Analyses of short term trends in vCJD have been published13 and currently indicate an approximate doubling in the number of cases of vCJD in the United Kingdom every 3 years. Longer term predictions of vCJD numbers have been more controversial with a wide range of future scenarios varying between a total of just over 200 cases,14 a few thousand cases15 and over 130 000 cases.16 This variation reflects the many uncertainties about BSE and vCJD, including the extent of human exposure to BSE, the level of the species barrier between bovine and human, and variations in host susceptibility—to date all tested cases of vCJD have been homozygous for methionine at codon 129 of the prion protein gene. One important variable in all estimates of vCJD numbers is the year cases first appeared. The paper by Hillier at al2 provides important support to the hypothesis that vCJD is a new disease which really did first appear in the mid-1990s.
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