NR ABFZ
AU Bennett,M.
TI Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. Incidence of bovine spongiform encephalopathy is higher in cows born after feed ban.
QU British Medical Journal 1996 Mar 30; 312(7034): 843-4
KZ BMJ. 1996 Jan 20;312(7024):180-1. PMID: 8563545
PT comment; letter
VT
EDITOR - R W Lacey could have made more of the data on the ages of cattle with bovine spongiform encephalopathy that he discusses.[i] The ban on the inclusion of recycled animal remains in agricultural feeds came into force in July 1988. Many calves born before this date might be expected eventually to develop the disease; those born later should have a greatly reduced, and diminishing, incidence of the disease. In his table Lacey compares two sets of data. The second column breaks down by age the numbers of cattle that were born before the ban in which the disease was diagnosed in 1989. The third column shows the breakdown for cattle that were born after the ban in which the disease was diagnosed in 1990-5. Assuming that each column gives a fair representation of the age Structure for the development of the disease, Lacey infers that this structure has changed little as a result of the ban.
The problem is that, for cattle born after the ban, there are many more animals that might develop the disease when young than that might develop the disease when old: crudely, we now have six annual cohorts of 1 year olds but only one annual cohort of 6 year olds. Assuming that the diagnoses for cows born after the ban were made between January 1990 and October 1995, I have calculated the number of annual cohorts of calves implicit in each age group of such diagnoses (table 1). The final column of the table then lists by age the number of diagnoses per annual cohort. These figures are thus equivalent to the column for the single year 1989.
The age structure of diagnoses can indeed be seen to have changed little. What is surprising, however, is that the incidence of the disease increased substantially after the ban. Among 5 year olds, for example, 1874 of those born in 1984 were affected; this figure increased to roughly 4353 of those born in 1989. Perhaps the Ministry of Agriculture, Fisheries and Food could supply the exact figures.
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Table 1-Numbers of cattle with bovine spongiform encephalopathy born before and after food ban was introduced in July 1988
Born before ban. Born after ban. Born after ban
disease disease (per annual
Age diagnosed diagnosed cohort
(years) 1989* 1990-5 of calves)
1- 1 1 0.2
2- 28 81 16.8
3- 586 2824 737.3
4- 2138 9820 3470.0
6- 1874 7966 4353.0
6- 667 2008 2419.3
7-8 125 9 62.9
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Total 5419* 22709 11049.5
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*England and Wales. Total number of British cases in 1989 was 7,627.[ii]
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M BENNETT Lecturer
Environmental Technology Centre, Department of Chemical Engineering, UMIST, PO Box 88, Manchester M6O 1QD
i. Lacey RW. Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. - BMJ 1996;312:180-1. (20 January)
ii. Almond JW, Brown P, Gore SM, Hofman A, Wientjens DPWM, Ridley RM, et al. - Creutzfeldt-Jakob disease and bovine spongiform encephalopathy: any connection? - BMJ 1995;311:1415-21(25 November.)
IN Der Autor interpretiert eine Tabelle von Lacey neu, die merkwürdigerweise nicht die jährliche Entwicklung der britischen BSE-Fallzahlen darstellt, sondern die 1989 diagnostizierten den in den 70 Monaten vom Januar 1990 bis zum Oktober 1995 beobachteten von nach dem Verfütterungsverbot vom Juli 1988 geborenen Tieren gegenüberstellt. Dabei wird nach den Lebensaltern der betroffenen Tiere differenziert, sodaß bei den letzten Jahrgängen die älteren Tiere natürlich unterrepräsentiert sind. Um die Vergleichbarkeit mit dem Beobachtungsjahrgang 1989 wieder herzustellen, rechnet er für jeden Geburtsjahrgang auf ein Beobachtungsjahr um. Danach stellt sich heraus, dass das Maximum tödlicher BSE-Infektionen bei den kurz vor, aber auch bei den kurz nach dem Verfütterungsverbot geborenen Rindern lag.
ZR 2 Zitate
MH Animal; *Animal Feed; Cattle; Encephalopathy, Bovine Spongiform/*epidemiology; Great Britain/epidemiology; Incidence; Legislation, Veterinary
SP englisch
PO England
OR Prion-Krankheiten 1