One out of the thousands of tiny proteins that are the molecular building blocks of every living cell twists out of its normal shape and becomes a silent killer. The rogue protein turns its neighbors into copies of itself. Each new recruit repeats the process. The number of rogue proteins grows faster and faster. Clumps of these misshapen proteins known as prions cause havoc in the human or animal nervous system.
Victims lose control of their minds and limbs.
In a few months they are dead, their brains riddled with spongelike holes. About 100 people, mostly in Great Britain, are known to have died from Creutzfeldt-Jakob. Two elderly Americans died of the disease in a Denver hospital last year. As a precaution, U.S. officials are quarantining sheep in Vermont and cows in Texas that were imported from areas of Europe that are infected with mad cow disease. Creutzfeldt-Jakob disease, mad cow disease, and a related sheep ailment called scrapie are especially scary, because there is no known cure, and because they can jump among species from sheep to cows, from cows to people.