Assumption that BSE originated from scrapie in sheep led to misjudgment

Assumption that BSE originated from scrapie in sheep led to misjudgment

June 23, 2001 British Medical Journal 322:1544 by M A Ferguson-Smith

EDITOR--In espousing the scrapie origin of bovine spongiform encephalopathy Brown fails to explain adequately why scrapie outside Britain has not led to bovine spongiform encephalopathy.1

Does Brown believe that scrapie "has mysteriously chosen the United Kingdom as its only geographical site and the early 1980s as its only historical occurrence" to appear in cattle? He explains that the comparatively high incidence of scrapie in sheep in the United Kingdom and the changes in rendering were responsible. This seems implausible, for reasons set out in the report of the BSE [bovine spongiform encephalopathy] inquiry.2

I am not aware of comparative data on the incidence of scrapie in the United Kingdom and abroad. Similar changes in rendering were occurring elsewhere, and no rendering process either before or since the emergence of bovine spongiform encephalopathy has been capable of completely inactivating scrapie.

The BSE inquiry was impressed by the more plausible alternative view that the agent giving rise to bovine spongiform encephalopathy was a novel strain of unknown origin that was pathogenic to humans. This view held that the strain arose in southern England in the 1970s and that the infection spread in waves through recycled infected cattle waste in meat and bonemeal. We will probably never know the origin of the agent--whether it arose in cattle or sheep or, indeed, any other species whose waste was incorporated into meat and bonemeal.

It was the assumption that bovine spongiform encephalopathy originated from an infection in sheep that led to the judgment that the risk of transmission to humans was remote. Brown's own research has indicated that scrapie was not linked to Creutzfeldt-Jakob disease, although humans have been exposed to scrapie for over 200 years.3

The uncertainties about the origin of bovine spongiform encephalopathy were not appreciated by many of those involved at the time. This is not a matter of criticism. As a result, however, the public was reassured unjustifiably.

M A Ferguson-Smith, emeritus professor of pathology. Department of Clinical Veterinary Medicine, Cambridge University, Cambridge CB3 0ES

1. Brown P. Regular review: Bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease. BMJ 2001; 322: 841-844[Full Text]. (7 April.)

2. BSE Inquiry. Report, evidence and supporting papers of the inquiry into the emergence and identification of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease (vCJD) and the action taken in response to it up to 20 March 1996. London: Stationery Office, 2000.

3. Brown P, Cathal F, Raubertas RF, Gajdusek DC, Castaigne P. The epidemiology of Creutzfeldt-Jacob disease: conclusion of a 15-year investigation in France and review of the world literature. Neurology 1987; 37: 895-904[Abstract].

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