But an expert in Penn State's College of Agricultural Sciences says American shoppers don't have to worry when buying beef.
Corrective measures seem to be working.
In North America, we've prohibited animal byproducts in feed, and banned importing these for any use in this country. In every case where the cause isn't known, samples of the animal are tested at the National Animal Disease Center in Iowa. To date, of more than 17,000 samples submitted, all have been negative. Because the disease has an incubation period of two to eight years, the control measures should finally be taking hold. But projections for BSE's future, he says, are hard to predict.