Why you give blood if eaten beef in Europe?

You should not donate blood if you have consumed beef from cattle raised in Europe in the past 12 months, due to the risk of variant Creutzfeldt-Jakob disease (vCJD). vCJD is a rare, fatal neurodegenerative disorder caused by a variant of the prion protein. It is believed that vCJD can be transmitted through the consumption of beef or other bovine products from cattle that are infected with bovine spongiform encephalopathy (BSE), commonly known as "mad cow disease".