Let me address some of the concerns that this action has raised. Mad cow disease first appeared there in 1985, a few years after a change had occurred in how cattle feed was prepared. In 1988, the use of certain animal products in cattle feed was banned, and the mad cow epidemic subsequently receded. New variant CJD appeared in the United Kingdom in 1995, ten years after the appearance of mad cow disease. New variant CJD is the human counterpart of mad cow disease.
Cattle develop symptoms about five years after exposure.
If the incubation period in humans is also five years, and no further transmission takes place, there could be less than 500 cases. However, if the incubation period is much longer, far more could be affected. A test to detect individuals at risk of developing new variant CJD might settle this issue, but that test is not yet available. There are other uncertainties as well. The new variant prion, for example, has been detected in the tonsils and the appendix of individuals before any symptoms of new variant CJD had developed.