There have been more than 190,000 confirmed BSE cases worldwide. Only four have occurred in the United States. The first two cases were in the state of Washington. Investigation showed that both cows were imported from Canada. The third case was a “downer” cow on a farm in Alabama. The herd of origin was never determined. A fourth case was detected in 2006 during a screening program in California. A very aggressive testing program plus strict enforcement of the preventive animal feeding rules have virtually eliminated mad cow disease from herds in the United States.