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Beware the Shape-shifter:
Seeing pink elephants

by Alicia P. Gregory

The most common human prion disease is Creutzfeldt-Jakob Disease (CJD). Like Alzheimer's, CJD is normally a disease of old age. It most frequently occurs in people in their 60s. Unlike Alzheimer's, CJD is rare: it kills one in a million people.

There are three types of this disease. The first, sporadic CJD, accounts for 85 percent of cases. Scientists call it sporadic because it occurs infrequently and in scattered cases. The rarest type, acquired CJD, is caused by infection, usually accidentally. Only 250 cases have been documented worldwide of people who developed CJD after medical procedures such as injections of human growth hormone from cadavers, corneal transplants, and infected surgical instruments. The last type of CJD is inherited in families carrying specific mutations in the prion protein gene and accounts for 15 percent of cases.

Between 1994 and 1996, 12 British teenagers were diagnosed with CJD. "To see CJD in people under 30 was the neuropathologist's equivalent of seeing a pink elephant," Telling says.

The timing of the diagnoses eerily coincided with Britain's outbreak of bovine spongiform encephalopathy (BSE), aka mad cow disease. "About 180,000 cattle have been killed by this disease, and recent estimates suggest that a least two million cattle were exposed to the agent," says Telling, a native of Great Britain with firsthand knowledge. Although he did all of his training and spent the majority of his career in the United States, Telling spent two years with the Medical Research Council in London at the height of the epidemic.

Scientists traced BSE back to prions in scrapie-infected sheep. Cattle were fed meat and bone meal made from sheep, and then cattle were fed meal from other cattle. "The disease was propagated by refeeding cattle to cattle in a cyclical process. Basically high-tech cannibalism," Telling says. "In 1996, Britain removed all animals over 30 months old from the food chain and established a ban on feeding ruminant-derived protein to other ruminants [deer, sheep, cows].

"Cattle are extensively consumed by the general public, so it's likely that BSE prions jumped from cattle to humans via the food chain." Science has since confirmed that this "new variant CJD" is actually the human form of BSE, Telling says. To date, 129 people in the U.K., six in France, and one in Hong Kong, Ireland, Italy, the United States, and Canada have been diagnosed with new variant CJD.

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