After reading this explanation, you will likely wish it was a fabrication. What you are about to read is true, and the names have not been changed.
The Foré tribe in New Guinea were cannibals up until the 1960's or so. So fearsome was their reputation that shipwrecked natives from the surrounding islands would swim the other way rather than land there.
The Foré, however, paid a heavy price for their choice of cuisine, being nearly destroyed as a people by Kuru, which results in total destruction of the brain. Kuru, you see, is transmitted by eating infected human brains, but you can also get it from muscle tissue (steaks are muscle), from transplants, from any infected animal product including soap and gelatin, and even from surgical instruments. The mechanism whereby Kuru spreads and causes disease is quite fascinating.
A parasite or bacterium uses its host as a sort of biological quarry for raw materials that it uses to survive and reproduce. A virus hijacks the cell's factories by replacing the master program on paper tape -- that is what DNA really is -- with its own program in order to make more programs which are distributed to other cells. Kuru is a a different animal entirely, being a prion, which is far more insidious than any other disease agent known to man.
Instead of being a living thing (like a bacterium or a parasite) or a program (like virus) a prion is a protein that reshapes normal proteins into a malignant form. That malignant form then modifies other proteins. This is how a prion reproduces. A prion is a simple form of replicating information against which the immune system really has no defense. (Some animals are more resistant since they make proteins which are not vulnerable to being reshaped, but this is not an immunological immunity.)
A virus has a protein coat surrounding and protecting genetic material. A prion has no genetic material to detect -- it is only a protein which makes it hard for the body to find. Prions are extraordinarily stable and can survive an autoclave and formaldehyde; they are vulnerable, at least as far as anyone knows, only to certain organic solvents at high temperature and pressures. Hardiness is one of the reasons prions are so easily spread.
Mad Cow Disease (Bovine Spongiform Encephalopathy -- BSE) is the same disease as Kuru. So is Scrapie in sheep. So is Transmissible Spongiform Encephalopathy (TSE) in mink. So, in all likelihood, are Alzheimers and a host of other human diseases including Creutzfeld-Jacob (CJD). Every mammal is vulnerable to Kuru, and it can jump from species to species with ease, as the recent epidemic of BSE in humans and cats in Britain clearly demonstrates.
There is speculation that prions were one of the first self-reproducing life forms and that prions have always been with mammalian life and that we will never get rid of them. (Three things in life are certain: death, taxes, and prions.)