What:

Bovine spongiform encephalopathy (BSE) - an aberrant pathology of the central nervous system in cows leading to the brain becoming spongy in appearance, i.e. a particular protein no longer folds correctly and the brain loses it's shape and becomes spongy due to holes. Prion disease: BSE and the forms of spongiform encephalopathy seen in other mammals are now known to be caused, at least in part, by prions. Prions are proteins that normally occur in the body, but sporadically undergo some form of conformational change and are no longer able to fulfill their structural function. Prions are not destroyed by heat or chemicals and inoculation with a prion causes more of the proteins in the body to becomes prions! There is some speculation that Alzheimer's may be a prion disease.

Where and when:

1732: Europe - Scrapie seen in sheep, possibly the emergence of a recessive defect due to inbreeding. The sheep had an itching disorder and scraped their skin off, then became wobbly and unable to walk and would collapse and die. Scrapie was a spongiform encephalopathy, called the "slow virus" it has an observed incubation of up to 8 years. 1950's: Kuru characterized in New Guinea Kuru tribe, a transmissable spongiform encephalopathy due to cannibalism of the dead. Another human form is Creutzfeldt-Jacob disease (CJD) which occurs sporadically at a very low rate due to improper protein folding, these defective proteins were discovered in 1997 and are called prions. A new concern in humans is variant CJD which may be associated with the transmission of prions from cows or other animals to humans. 1960's: Northwest United States - Chronic wasting disease (CWD) seen in deer and elk, spread to Canada. 1982: Scrapie in Oklahoma. Animals had to be destroyed either by burning or burying, prions are nearly indestructible. 1986: BSE in British cows. 2003: BSE in U.S. cows.

The food supply

The fear of mad cow disease lies in its transmission to humans from eating infected meat. Prions are resistant to heat and there is little known about them. An increase in the rate of CJD in Britain has raised questions about the extent of our knowledge. Proper butchering techniques that prevent the nervous system organs and those known to contain the prions from coming into contact with the edible parts, should be enough to prevent the spread. Cows that exhibit any of the symptoms of the disease are supposed to be removed from the food chain and incinerated. It is also illegal to feed cows the parts of other animals, called ruminant feed and bone meal.