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By Maggie Fox, Health and Science Correspondent


WASHINGTON (Reuters) - Cannibalism may have spread a deadly brain-wasting disease among human populations thousands of years ago -- and may have eventually helped people evolve a resistance to such diseases, researchers report.


Genetic studies show that humans around the world have a similar predisposition to resist the brain-destroying disease called Creutzfeldt-Jakob disease, the team at University College London said on Thursday.


CJD occurs naturally in about one in a million people. It is incurable and always fatal, chewing holes in the brain that lead to dementia and death.


A closely related disease called kuru was once common in Stone Age populations in Papua New Guinea in the first half of the 1900s, and was closely linked to the practice of eating the dead in rituals. Scientists quickly determined that eating brains could cause various forms of CJD.


"There is extensive anthropological evidence that cannibalism is not just some rarity that happened in New Guinea," John Collinge, who led the study, said in a statement.


Anthropologists debate whether prehistoric humans ate one another, but Collinge and colleagues, reporting in the journal Science, say they have new evidence they did.


Sheep have their own version of the disease called scrapie, and it passed into cattle herds when farmers started feeding cattle ground-up sheep carcasses.


Since the 1990s, a new form has been found in people, almost all of them in Britain, and linked to the epidemic of bovine spongiform encephalopathy, or mad cow disease.


People can get a variant of CJD from eating BSE-infected beef. It is not clear how widespread the disease will be, as it can take decades to develop. About 130 people, mostly in Britain, have died from the new variant CJD.


Researchers say CJD, BSE and related diseases are all caused by a crumpled protein called a prion. They have also found that some people have a genetic predisposition to prion diseases, but many have a genetic resistance.


GENES AND CANNIBALS


Collinge and colleagues in London, Papua New Guinea and Australia did a genetic analysis of the Fore people known for their funerary feasts.


Australian colonists put an end to the cannibalistic rituals but many people who ate human flesh as children survive. Mostly women and children ate the human flesh, the researchers said.


"At its peak, kuru killed around one percent of the population annually and some villages were almost devoid of young adult women," they wrote.


They got blood samples from Kuru women over the age of 50 and did genetic analysis. They found a genetic mutation known to protect against prion disease was much more common in these women, who would have survived despite being cannibals, versus the living population of younger Kuru people.


This suggests the Kuru women who lived to age 50 and beyond survived because of the genetic mutation.


Collinge's team also looked at the genetics of people around the world, and found that mutations protecting against prion diseases were common, and found with just about the same frequency everywhere.


The evidence suggests the genetic mutations date back 500,000 years, they said.

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