Prion diseases, a group of uncommon and deadly brain diseases, can be spread by eating the contaminated flesh of humans or other animals. The human brain is more contaminated with prions than other body parts, though bone marrow, the spinal cord and the small intestine also contain these fatal brain-eating malformations. Prion diseases occur when the prion protein misfolds, causing a cascade of misfolding prion proteins that clump in the brain and damage or destroy nerve cells, creating sponge-like holes. Current examples include kuru and Creutzfeld-Jacob disease in humans, and mad cow disease in animals, both of which cause brain deterioration, loss of motor control and ultimately death.

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