The deadly human form of mad cow disease, vCJD, may have infected far more people than previously thought, suggests a new study in the British Medical Journal.

Variant Creutzfelt-Jakob disease is linked to eating meat infected with bovine spongiform encephalopathy (BSE), also known as mad-cow disease. A rogue version of a prion protein proliferates in the brain, leading to distressing mental deterioration, loss of motor control, and eventually death.