The move would expand restrictions on animal feed imposed after an outbreak of bovine spongiform encephalopathy, or "mad cow disease," in Britain in the 1980s and 1990s. Whether it is a disease of humans, cows, sheep (in which it is known as scrapie,) mink (transmissible mink encephalopathy) or deer and elk (chronic wasting disease), spongiform encephalopathy is a gruesome way to die, experts say.

Vaguely understood proteins known as "prions" appear to attack the central nervous system and cause the brain to deteriorate, riddled with wormhole-like formations. It is invariably fatal, preceded by confusion, dementia and paralysis. Prions, proteins which occur normally in virtually all animals, appear to become lethal when something happens to cause them to "fold," scientists say.

In addition to causing the sponge-like holes to appear in brain tissue, folded prions seem to cause other normal prions to take on the lethal folded form.

So far, no one knows why any of this happens.

However, the damaging prion form can withstand unusual stress, including rendering or even being stored in formaldehyde for years, say researchers at the National Institute of Neurological Disorders and Stroke.

Since the prions appear to concentrate in certain organs, such as the brains, spinal cords and some digestive organs, the British outbreak led to concern that persons who ate beef containing these tissues had been "infected" with the disease. Autopsies revealed abnormal prions in the brains of victims.

The disease appears to have spread to at least 131 human victims, almost all of them in the United Kingdom, in the form of a new variant of the age-old Creutzfeldt-Jakob Disease.

Although it is not a reportable disease, the Centers for Disease Control and Prevention in Atlanta says that only one case of the variant CJD is known to have appeared in the United States. The victim was a former resident of the United Kingdom.

The disease occurs spontaneously in about one of every 1 million human beings, according to CDC, but some medical professionals think it is more common than that. Some cases appear to be hereditary.

To get better information on the extent of the disease in America, CDC helped establish the National Prion Disease Pathology Surveillance Center at Case Western Reserve University in Cleveland.

Fears about the variant in the United States are behind the Food and Drug Administration's request for industry comments on how difficult and how costly it would be to remove brains and spinal cords from rendered products. After reviewing this information, officials said, they will consider whether to propose a rule requiring the step.

Animal waste parts left over from meat and poultry slaughtering and processing are commonly added to the feed of other animals.

Most of those animals end up on American dinner or restaurant tables. Some parts are again left over, and added to the feed of the next generation of animals.

This process frightens some CJD experts and has caused consumer activists to demand the removal of all rendered animal parts from the feed of animals Americans eat.

The FDA already prohibits the inclusion of rendered parts of ruminants and minks from feed given to other ruminants, primarily cattle, sheep and goats.

But feed manufacturers are free to put cooked-down chicken and pig parts in cattle feed. Cow parts can be legally added to chicken and pig feed.

Cooked down and ground into a brown sugar-like powder, the leftover parts are used to enhance the protein content of livestock feed.

Requiring rendering plants to remove brains and spinal cords _ known as "high risk" tissues _ from all rendered products would be "a good step, but it is not enough," said Jean Halloran, a policy specialist with the Consumers Union, the organization that publishes Consumer Reports magazine.

"It does not keep deer and elk out of the feed stream, for example, and it doesn't ban the practice of feeding cow parts to chicken and pigs or chickens and pigs to cows," she said.

She said the carcasses of "road kill" deer often are taken to rendering plants for disposal.

A German company, ScheBo Biotech, which has an office in Marietta, Ga., says it has developed a test for "the accidental admixture of brain and spinal cord in meat products."

The company claims the test can protect people from consuming food tainted by brain and spinal cord material affected by bovine spongiform encephalopathy.

However, Halloran said this would not protect against prions sometimes found concentrated in other animal parts, such as spleens, which find their way into sausage and ground meat.

"I would say, just don't eat hamburgers and sausage when you go to London," she said.

On the Web:

The National Prion Disease Pathology Surveillance Center: www.cjdsurveillance.com

Jeff Nesmith's e-mail address is jeffn(at)coxnews.com