WASHINGTON (AP) - A study in monkeys suggests that older individuals are just as susceptible as the young to contracting mad cow disease.

The study, appearing Tuesday in the Proceedings of the National Academy of Sciences, involved injecting monkeys with new variant Creutzfeldt-Jakob Disease, waiting for the animals to develop disease symptoms, and then performing autopsies on their brains.

Older monkeys, the researchers found, developed brain plaques and disease just as readily as the younger monkeys, although the disease was more severe in the younger animals.

"This is important with regard to the fact that vCJD (variant Creutzfeldt-Jakob Disease) has been diagnosed mainly in teen-agers and young adults," the authors report.

The research was conducted by scientists in France and the United Kingdom.

Dr. Paul Brown, an expert on CJD at the National Institutes of Health, said the discovery that vCJD can affect older people "is bad news."

"The study showed that young and old monkeys were equally susceptible," said Brown. "That strikes a warning note about infection in humans and the possibility that older people will become infected.

"It makes you worry more that over the course of time, older people will come down with the disease," he said.

Variant Creutzfeldt-Jakob Disease, or vCJD, has been linked directly to eating meat from cattle infected with bovine spongiform encephalopathy, which is commonly called "mad cow disease." At least 80 people in Europe have died of vCJD since the mid-1990s.

Mad cow disease destroys the brain, causing infected animals to act in bizarre ways. It was first diagnosed in Britain where about 177,000 cattle were found to be infected. Cases also have been reported in France, Italy, Germany and Spain. Thousands of cattle, in herds where mad cow was discovered, have slaughtered to prevent spread of the disease.

It is estimated that about one million pounds of contaminated cattle may have entered the human food chain, and authors in the study estimate that this could result in up to 136,000 cases of vCJD. Because of a long disease incubation period, it may be years before the exact toll from vCJD is determined.

Although another form of Creutzfeldt-Jakob, called "sporadic," occurs in the U.S., it is not linked to eating meat. There have been no identified cases of vCJD, the form of the disease linked to beef, in the U.S.

BSE is thought to have spread to cattle through the use of feed enriched with body parts from sheep infected with scrapie, a related disease.

The FDA in 1997 banned the use of any proteins from cows, sheep, goats, deer or elk, all of which get BSE-like diseases, from being used in feed for cattle, sheep or goats. The agency in January, however, said that 30 percent of U.S. plants that render animal products into livestock feed had no system to prevent the inappropriate addition of animal body parts into feed.

All of these brain-wasting diseases, in animals and humans, are caused by a prion, a misshapen protein that alters the shape of other proteins, and causes the formation of cavities in the brain.

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