For several years the Red Cross would not accept blood from anyone who had spent 6 months or more since Jan. 1980 in Europe, because of the mad cow issue. I had spent 7 months in Europe in 1980 so I could not donate, but later they relaxed the rule so now I can give again. I don't know if they have any documented cases of a person getting mad cow disease from a blood transfusion.
Meanwhile, people who have lived all their lives in Europe can donate blood to other people.