Every time I donate I trip one of the "mad cow disease" questions. If they think you've spent substantial time in Europe they suspect you may have been exposed to Creutzfeldt-Jakob disease. The problem with CJD is that it's not screenable in the blood (unlike HIV these days and they still ask questions and exclude those with risk fort hat). Being in the military in the UK is one of the very questions they ask on the CJD screen.