School ofClinical. Veterinary Medicine,. Cambridge CB3 OES. R M Ridley, head ofteam. H F Baker ... high the minimum incubation period was less than four.
France was five, in Germany two, and in Italy three.6 Bovine spongiform encephalopathy has not been reported in these countries. This suggests that the number of cases in farmers in Britain is not surprising and need not be related to bovine spongiform encephalopathy. The only known cases of acquired spongiform encephalopathy in humans have involved ingestion, injection, or other internal contamination with material associated with human brain, and brain is the only tissue consistently infectious in bovine spongiform encephalopathy. If these farmers had been at risk from handling cattle feed one would expect feed producers to have been at greater risk, and if the farmers had been at risk from handling affected cattle one would expect abattoir workers to have 1 Alperovitch A, Brown P, Weber T, Pochiari M, Hofman A, Will R. Incidence been at greater risk. There is no evidence that these of Creutzfeldt-Jakob disease in Europe in 1993. Lancet 1994;343:918. occupational groups are at higher risk of contracting 2 Delasnerie-Laupretre N, Poser S, Pocchiari M, Wientjens DPWM, Will R. Creutzfeldt-Jakob disease. Creutzfeldt-Jakob disease in Europe. Lancet 1995;346:898. 3 Masters CL, Harris JO, Gajdusek DC, Gibbs CJ Jr, Bernoulli C, Asher DM. Four cases of apparently idiopathic CreutzfeldtCreutzfeldt-Jakob disease: pattems of worldwide occurrence and the signifiJakob disease have been reported in teenagers in cance of familial and sporadic clustering. Ann Neurol 1979;5:177-88. 4 Wienejens DPWM, Davanipour Z, Hofinan A, Kondo K, Matthews WB, Will continental Europe and the United States.7-'0 Since RG, et at. Risk factors for Creutzfeldt-Jakob disease: a reanalysis of casethese cases cannot be related to bovine spongiform control studies. Neurology (in press). 5 Hofnan A. Risk of Creutzfeldt-Jakob disease in relation to animal spongiform encephalopathy, the occurrence of Creutzfeldt-Jakob encephalopathies: a collaborative study in Europe. Eur J Epidemiol 1991;7: in two teenagers in Britain" 12 does not disease 466-8. make a link with bovine spongiform encephalopathy obligatory. However, these two cases are extremely unusual both in the ages at onset and in the reported Who gets Creutzfeldt-Jakob disease? neuropathology. A greater appreciation of the variety of clinical presentations, neuropathology, and age at onset of Creutzfeldt-Jakob disease in recent yearsR M Ridley, H F Baker together with the heroic attempts of the National CJD Surveillance Unit to identify all cases-should lead Whenever an unusual case of Creutzfeldt-Jakob to greater ascertainment, particularly of those cases disease is reported in Britain someone asks: "Is this which are unusual. We hope that this explains the the beginning of the end-are we all going to die of detection of these two cases in young people. BSE?" It is a commonly held view that the incubation MP. Kuru-implications of its transmissibility for the interpretation of period for spongiform encephalopathy in humans is at 1 Alpers its changing epidemiological pattern. In: Bailey OT, Smith DE, eds. The least one to two decades. This is a misconception. For central nervous system-some experimental models of neurological disease. Baltimore, MD: Williams and Wilkins, 1968:234-5 1. kuru, when the dose of infectivity by the oral route was EM, Masters CL, Alpers MP, Kavan J, Gajdusek DC. A clinicohigh the minimum incubation period was less than four 2 Scrimgeour pathological study of a case of kuru.JNeurolSci 1983;59:265-75. years and the median ranged from less than five years to 3 Davies PTG, Jahfar S, Ferguson IT. Creutzfeldt-Jakob disease in individual occupationally exposed to BSE. Lancet 1993;342:680. nine years (judged by the minimum ages at onset at the SJ, Yuill GM, Esmonde TF, Estibeiro P, Ironside JW, Bell JE, et al. height of the epidemic).' However, the incubation 4 Sawcer Creutzfeldt-Jakob disease in an individual occupationally exposed to BSE Lancet 1993;341:642. [letter]. period can be as long as 30 years (judged by the ages of 5 Smith PEM, Zeidler M, Ironside JW, Estibeiro P, Moss TH. Creutzfeldtthe most recent cases).' Jakob disease in a dairy farmer. Lancet 1995;346:898. 6 Delasnerie-Laupretre N, Poser S, Pocchiari M, Wientjens DPWM, Will R. While experimental transmission of spongiforn Creutzfeldt-Jakob disease in Europe. Lancet 1995;346:898-9. encephalopathy across species generally results in 7 Monreal J, Collins GH, Masters CL, Fisher CM, Kim RC, Gibbs CJ, et aL increased incubation times, this is because the "species Creutzfeldt-Jakob disease in an adolescent.JNeurolSci 1981;52:341-50. P, Cathala F, Labauge R, Pages M, Alary JC, Barton H. Epidemiologic barrier" increases the dose required, so that fewer 8 Brown implications of Creutzfeldt-Jakob disease in a 19-year-old girl. Eur J individuals are affected. It is now six to nine years since Epidemiol 1985;1:42-7. the general public was at greatest risk of consuming 9 Bernan PH, Davidson GS, Becker LE. Progressive neurological deterioration in a 14-year-old girl. Pediatric Neuroscience 1988;14:42-9. meat products containing brain tissue from cattle 10 Kulczycki J, Jedrzejowska H, Gajkowski K, Tamowska-Dziduszko E, Lojkowska W. Creutzfeldt-Jakob disease in young people. Eur Y Epidemiol incubating bovine spongiform encephalopathy (that is, 1991;7:501-4. between the emergence of this disease in 1986 and the 11 Britton TC, Al-Sarraj S, Shaw C, Campbell T, Collinge J. Sporadic Specified Offals Ban of 1989), so it is already clear Creutzfeldt-Jakob disease in a 16-year-old in the UK. Lancet 1995;346:1 155. 12 Bateman D, Hilton D, Love S, Zeidler M, Beck J, Collinge J. Sporadic that a substantial proportion of the population will not Creutzfeldt-Jakob disease in a 18-year-old in the UK. Lancet 1995;346: be affected. Nonetheless, the occurrence of only a 1155-6. handful of cases of human spongiform encephalopathy resulting from exposure to bovine spongiform encephalopathy would be a tragedy, and any possible Furrowed brow over mad cow case warrants close examination. It is, however, another misconception to suppose that every case of Creutzfeldt-Jakob disease must have been caught from G W Roberts somewhere. About 15% of cases are wholly genetic in origin, and in nearly all of the remaining cases persistent and extensive epidemiological investigation Anxieties over the possibility that material from or has failed to find a contamination event, leading to the contact with cows infected with bovine spongiform proposition that these cases are idiopathic. It is against encephalopathy might cause Creutzfeldt-Jakob disease this background that the occurrence of Creutzfeldt- revolve around three questions. Jakob disease in four farmers and two teenagers should be considered. The four farmers had ages at onset and clinical Could it happen? Bovine spongiform encephalopathy in cows, scrapie pictures consistent with idiopathic Creutzfeldt-Jakob disease.'" During a similar period the number of in sheep and experimental animals, and Creutzfeldtfarming employees with Creutzfeldt-Jakob disease in Jakob disease are all caused by the same class
Although the occurrence of Creutzfeldt-Jakob disease in four dairy farmers in Britain is clearly a matter of concern, the current evidence from the European surveillance study suggests that there is no higher risk of the disease in British dairy farmers than in farmers in other European countries. Furthermore, the overall incidence of Creutzfeldt-Jakob disease is similar in the five European countries, while there is a substantial difference in the incidence of bovine spongiform encephalopathy. Taken together, the epidemiological evidence to date does not point to a causal link between bovine spongiform encephalopathy and Creutzfeldt-Jakob disease but, unfortunately, does not strongly reject that possibility either.
MRC Comparative Cognition Team, Department of Experimental Psychology, School of Clinical Veterinary Medicine, Cambridge CB3 OES R M Ridley, head ofteam
H F Baker, senior scientific
officer Molecular Neuropathology, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park-North, Harlow CM19 SAW G W Roberts, professor BMJ VOLUME 311
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