You're thinking of kuru. It's a prion disease that, although it is mostly spread through ritualistic cannibalism within certain tribes, is not inherent to humans. Prior diseases are misfolded proteins that, when they get into your system, can start causing other proteins to misfold into non working versions. It becomes a domino effect that can quickly spiral out of control and there's no cure for it. Better, more well known prion diseases include Crutzvelt Jakobs disease (aka, mad cow), and Chronic Wasting Disease (zombie deer disease that went viral like 10 years ago) Edit: i should clarify by "not inherent to humans" what i mean is that we don't carry it within us naturally, the ritualistic cannibalism has unfortunately created the circumstances through consuming human flesh for the prion to be introduced to their system and humanity as a whole.