A filtering device developed by a Long Island, N.Y., company is being tested in Britain for its ability to rid the blood supply of the misfolded proteins responsible for the human form of mad-cow disease, variant Creutzfeldt-Jakob disease (CJD).

The filter, developed by the Pall Corp., clears donor blood of abnormal prion proteins. The infectious protein has led to the deaths of 172 people, mostly in Britain and Europe, since 1995.

Variant CJD develops in humans who eat meat from sick animals. Because people can harbor the infectious proteins for years without symptoms, scientists worry the donor blood supply could become a source of transmission.

There are no blood tests to identify abnormal prions. Dr. Ermias Belay, a medical epidemiologist at the Centers for Disease Control and Prevention, said scientists find it hard to differentiate between the normal prion protein and its abnormal form.

Pall's filter traps infectious prions in red blood cells. It strips the abnormal protein from blood, but it isn't a test that could be used to detect abnormal prions in a small sample. The company plans to submit studies of its system to the U.S. Food and Drug Administration (FDA) next year.

Dr. David Asher, head of the FDA division of emerging and transfusion-transmitted diseases, said, "physical removal of vCJD from blood appears to be the most promising line of attack" but stressed he has not evaluated any studies by Pall.

He said the U.S. is safeguarding its blood supply by refusing blood donations from anyone who spent three months or longer in Britain between 1980 and 1996.

"It's a risk-reduction, not a risk-elimination policy," he said.

Last year, British pathologists tested more than 12,000 tissue specimens from people age 20 to 29 who were having their tonsils and adenoids removed. They found three samples that contained the abnormal prion protein. Based on that finding, British pathologists calculated that 237 of every million young adults in Britain could have been exposed to infectious prion protein from eating infected beef. The number is still being debated.

"It seems high, considering that there has been a peak in the U.K. [United Kingdom] cases," the FDA's Asher said.

The sporadic form of CJD is rare, one in a million, and is not tied to consuming infected meat. The sporadic and the new variant form destroy the brain, causing dementia, psychosis, an inability to move or speak, and death.

Many labs are working on a CJD blood test. It would allow scientists to identify prion disease in cattle before it enters the food chain, Pall's principal scientist Samuel Coker said.

Now, only cows that show neurological symptoms are slaughtered and tested.