Abstracts
Résumé
Les modélisations de l’épidémie du variant de la la maladie de Creutzfeldt-Jakob (vMCJ) dû à l’agent de l’encéphalopathie spongiforme bovine (ESB) font toutes appel à un « rétro-calcul » qui relie par une équation mathématique simple: (1) le nombre de personnes infectées; (2) la distribution des dates d’infection; et (3) la distribution de la durée d’incubation. Les modèles se distinguent par les hypothèses et les techniques utilisées pour définir ces trois paramètres inconnus. En ce qui concerne la durée d’incubation, certains modèles font appel à des scénarios fixant arbitrairement sa valeur moyenne et sa variabilité; d’autres, plus récents, cherchent à les estimer en s’appuyant sur l’incidence du vMCJ entre 1995 et 2001. Malgré de nombreuses différences méthodologiques, les résultats des modélisations sont très cohérents. Pour des durées d’incubation de 15 à 20 ans, valeur obtenue par tous les modèles ayant cherché à estimer ce paramètre à partir de l’incidence du vMCJ, les cinq modèles prédisent une épidémie de 500 à 2000 cas au Royaume-Uni.
Summary
The back-calculation technique is used in all studies aimed at predicting the future incidence of the variant Creutzfeldt-Jakob disease (vCJD) caused by the agent of bovine spongiform encephalopathy (BSE). The back-calculation method uses a simple mathematical equation which relates (1) the number of infected persons ; (2) the distribution of infection times ; and (3) the incubation period distribution. The different studies considered in this review differ essentially in their assumptions and in the techniques used to assign values to the unknown parameters. For the incubation period distribution, some studies use scenario based-technique analysis where the mean and the variance are arbitrarily fixed. In other recent studies, these parameters are estimated using the observed incidence of vCJD between 1995 and 2001. Despite several methodological differences, the results obtained from these different studies are consistent. Albeit the methodology used, for mean incubation periods between 15 and 20 years - the best estimates found in the « estimation » studies - the five models considered in this review predict an epidemic size between 500 and 2000 cases in the United Kingdom.
Appendices
Références
- 1. Will RG, Ironside JW, Zeidler M, et al. A new variant Creutzfeldt-Jakob disease in the UK. Lancet 1996; 347: 921-5.
- 2. Chazot G, Broussolle E, Lapras C, Blättler T, Aguzzi A, Kopp N. New variant of Creutzfeldt-Jakob disease in a 26-year-old French man. Lancet 1996; 347: 1181-8.
- 3. Bruce M, Will RG, Ironside JW, et al. Transmissions to mice indicate that ‘new variant’ CJD is caused by the BSE agent. Nature 1997; 389: 498-501.
- 4. Lasmézas CI, Deslys JP, Demalmay R, et al. BSE transmission to macaques. Nature 1996; 381: 743-4.
- 5. Hill AF, Desbruslais M, Joiner S, et al. The same prion strain causes vCJD and BSE. Nature 1997; 389: 448-50.
- 6. Gore SM, Bingham S, Day NE. Age related dietary exposure to meat products from dietary surveys of teenagers and adults in the 1980s and 1990s. Br Med J 1997; 315: 404-5.
- 7. Cousens S, Smith PG, Ward H, et al. Geographical distribution of variant Creutzfeldt-Jakob disease in Great Britain, 1994-2000. Lancet 2001; 357: 1002-7.
- 8. Bryant G, Monk P. Summary of the final report of the investigation in the North Leicesterhire cluster of variant Creutzfeldt-Jakob disease. Leicestershire NHS Health Authority, 2001. http://www.leics-ha.org.uk (consulté le 7 octobre 2002).
- 9. Andrews NJ, Farrington CP, Cousens SN, et al. Incidence of variant Creutzfeldt-Jakob disease in the UK. Lancet 2000; 356: 481-2.
- 10. The EuroCJD Group. Genetic epidemiology of Creutzfeldt-Jakob disease in Europe. Rev Neurol (Paris) 2001; 157: 633-7.
- 11. Huillard d’Aignaux J, Costagliola D, Maccario J, et al. Incubation period of Creutzfeldt-Jakob disease in human growth hormone recipients in France. Neurology 1999; 53: 1197-201.
- 12. Cousens SN, Vynnycky E, Zeidler M, Will RG, Smith PG. Predicting the CJD epidemic in humans. Nature 1997; 385: 197-8.
- 13. Ghani AC, Ferguson NM, Donnelly CA, Anderson RM. Predicted vCJD mortality in Great Britain. Nature 2000; 406: 583-4.
- 14. Huillard d’Aignaux J, Cousens SN, Smith PG. Predictability of the UK variant Creutzfeldt-Jakob disease epidemic. Science 2001; 294: 1729-31.
- 15. Valleron AJ, Boelle PY, Will RG, Cesbron JY. Estimation of epidemic size and incubation time based on age characteristics of vCJD in the United Kingdom. Science 2001; 294: 1726-8.
- 16. Ferguson NM, Ghani AC, Donnelly CA, Hagenaars TJ, Anderson RM. Estimating the human health risk from possible BSE infection of the British sheep flock. Nature 2002; 415: 420-4.
- 17. Cooper JD, Bird SM, De Angelis D. Prevalence of detectable abnormal prion protein in persons incubating vCJD: plausible incubation periods and cautious inference. J Epidemiol Biostat 2000; 5: 209-19.
- 18. Ghani AC, Ferguson NM, Donnelly CA, Hanegaars TJ, Anderson RM. Estimating the number of people incubating variant CJD. Lancet 1998; 352: 1353-4.
- 19. Hill AF, Butterworth RJ, Joiner S, et al. Investigation of variant Creutzfeldt-Jakob disease and other human prion diseases with tonsil biopsy samples. Lancet 1999; 353: 183-9.
- 20. Ironside JW, Hilton DA, Ghani AC, et al. Retrospective study of prion-protein accumulation in tonsil and appendix tissues. Lancet 2000; 355: 1693-4.
- 21. Brookmeyer R. Reconstruction and future trends of the AIDS epidemic in the United States. Science 1991; 253: 37-42.
- 22. Huillard d’Aignaux J, Cousens SN, Maccario J, et al. An analysis of the incubation period of kuru by sex and age at infection. Epidemiology 2002 (sous presse).
- 23. Lloyd SE, Onwuazor ON, Beck JA, et al. Identification of multiple quantitative trait loci linked to prion disease incubation period in mice. Proc Natl Acad Sci USA 2001; 98: 6279-83.