BMJ 1996;312:843 (30 March)

Letters

Cohort study of cows is in progress

EDITOR,--R W Lacey's letter makes no reference to any scientific paper on the epidemiology of bovine spongiform encephalopathy.1 As a result it contains too many omissions, errors, and misconceptions to pass into the literature unchallenged.

Lacey's description of the cohort study to examine the risk of maternal transmission is incorrect. This study is comparing the incidence of bovine spongiform encephalopathy in offspring of dams that developed clinical signs of the disease and in offspring of dams that reached at least 6 years of age without developing clinical signs. Three hundred pairs of animals are involved, and the members of each pair were born in the same calving season and herd. The criteria for purchase, between July 1989 and February 1990, were that the animals had been weaned, females were virgin, males had been castrated, and documentation for the animals' provenance was available. Age at purchase ranged from 2 to 24 . . . [Full text of this article]


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Aetiology of scrapie in certain circumstances is not evidence against another aetiology in different circumstances
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