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Hundreds of people fell ill, after eating contaminated meat, with the disorder caused in humans — named variant Creutzfeldt-Jakob disease — and many died.

The American Red Cross, which provides about 40% of the U.S. supply, last month began accepting donors previously deferred because of the risk of mad cow disease, formally known as variant Creutzfeldt-Jakob disease, or vCJD.

In humans, mad cow disease is known as variant Creutzfeldt-Jakob disease, and it has killed more than 220 people worldwide since the 1990s.

When this illness crossed the species barrier from animal to human in 1996, it took the form of variant Creutzfeldt-Jakob disease, or vCJD.

Like both bovine spongiform encephalopathy — also known as mad-cow disease — and variant Creutzfeldt-Jakob disease in humans, CWD occurs when cellular proteins called prions bend into an abnormal shape, inducing neighbouring, healthy proteins to do the same.