BSE controls final report, 20 December 2000, section 6, BSE in cattle
19.BSE was first confirmed in 1986 and was made a notifiable disease in June 1988. There have been over 179,000 confirmed cases to date. The epidemic in cattle peaked at an annual total of over 36,000 cases in 1992/93 and the number of new cases is currently at the lowest level since recording started in 1988 (about 1,500 confirmed cases so far this year). At its peak the epidemic affected approximately one per cent of adult breeding cows per year. It has been estimated14 that over 900,000 animals were infected between 1974 and 1995, of which approximately 750,000 entered the food chain. There is considerable evidence that in BSE-infected cattle the abnormal prion is confined almost entirely to the nervous system, unlike the situation in scrapie in sheep (see paragraph 23 and Annex H). Various measures have been introduced to control BSE, including the slaughter of and compensation for affected animals and the culling of their cohorts15 (born between 1989 and 1993) and offspring (born after 1 August 1996). Models of the epidemic indicate that although numbers will continue to decline rapidly in the next 2-3 years, there may then be a long and slower decline, attributable to cases arising from dam to calf transmission of the BSE agent. Existing and future surveys using diagnostic tests will provide an independent assessment of the progress of the epidemic.
20.In July 2000 the EU Scientific Steering Committee (SSC) adopted an Opinion16 on the geographic risk of BSE in all EU Member States and certain third countries. It determined four categories17 of risk and allocated countries to one of the four categories. The UK has been assessed as falling in Category IV, the highest risk category. The threshold for inclusion in Category IV is an incidence of more than 100 confirmed BSE cases per million within the cattle population over 24 months of age in the country, calculated over the last 12 months. It is expected that the epidemic will have declined sufficiently for the United Kingdom to be classified in a lower risk category by 2002. Factors other than confirmed cases (such as imports of contaminated feed or infected animals and the possibility of cross-contamination of cattle feed with other feeds that contain mammalian MBM) were also taken into account by the SSC in determining risk category.
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14 - Anderson et al Transmission dynamics and epidemiology of BSE in British cattle Nature, 382, 779-788 (1996)
15 - 'Cohort' is the term used for groups of animals believed to have shared the same contaminated feed as confirmed BSE cases in the first six months of life.
16 - Final Opinion of the Scientific Steering Committee on the Geographical Risk of Bovine Spongiform Encephalopathy (GBR) (Adopted on 6 July 2000)
17 - The categories relate to the presence of one or more cattle clinically or pre-clinically infected with the BSE agent in a geographical region/country. For Category I this is assessed as "Highly unlikely", for Category II as "Unlikely but not excluded", for Category III as "Likely but not confirmed or confirmed, at a lower level" and for Category IV as "Confirmed, at a higher level".