The Biology of Cannibalism

 

            Kuru was a disease of certain South Pacific islanders.  On the death of a chief, the members of the tribe would eat his brain as a ritual to encourage his spirit to carry on for their benefit.  Years later, many of those who had eaten the brain began to have clumsiness and dementia progressing gradually to death.  Mankind has imposed a similar burden of cannibalism on cows by feeding the animal waste from slaughter-houses.  This is the origin of mad cow disease (bovine spongiform encephalopathy).

            Creutzfeldt-Jacob disease is a rare affliction of man world wide with the symptoms of Kuru.  It does not seem to be contagious except that it has been transmitted by corneal transplants and several years ago by injected human growth hormone when it was still prepared from human pituitary glands.  New variant Creutzfeldt-Jacob disease occurs in younger people than the classic disease and only in countries afflicted with mad cow disease, surely from eating meat from diseased cows.  Scrapie is the corresponding disease in sheep, well know for many years.  Presumably mad cow disease originated from feeding cows slaughter house material from  cows and initially perhaps from sheep with scrapie.    Nothing  resembling  transmission of scrapie to man has been recognized.  Furthermore, Creutzfeldt- Jacob disease has not been more prevalent in parts of the world with many sheep, endemic scrapie, and much mutton consumption.

            Until recent years these diseases were all called slow virus diseases because of no bacteria associated with them and because of their long incubation period and indolent clinical course.  Modern virology has found no virus in any of these cases and it has been shown that material free of DNA and RNA can cause these diseases by injection.  DNA and RNA are the stuff of inheritance for all terrestrial life including viruses.  Furthermore sufficient heating to kill all life does not prevent the experimental transmission of these diseases.  So we were left with the enigma of a seemingly infectious process with no prospect of discovering an infectious agent.  Enter Stanley B. Prusiner.  He demonstrated that these diseases depend upon an abnormally folded structural protein of the brain and spinal cord, and called these abnormally folded but otherwise chemically normal proteins prions and the diseases prion diseases.  Stanley B. Prusiner received a Nobel prize for this in 1997.  A few molecules of the abnormally folded protein cause the already present normal structural protein to assume the abnormally folded form.  When enough of the brain structure gradually becomes abnormal, the symptoms of incoordination and dementia appear.  We know from people who are exquisitely allergic, such as peanut allergy, that a few protein molecules must survive digestion.  Presumably the same thing happens occasionally when prions are present in food.  Further evidence of the correctness of the above is that prion protein survives heat sufficient to kill all living things (cooking won’t suffice).

            Finally, there have been no recognized cases of mad cow disease or new variant Creutzfeldt-Jakob disease in the USA.  Informed citizens can help to keep it this way.  Farmers can do this easily by selecting a healthy calf, feeding it properly, having it custom butchered, and grinding their own hamburger (normal cleaning of a grinder does not destroy prions).

April 2, 2001