By Marc Kaufman

The Food and Drug Administration yesterday proposed tightening the rules governing who can donate blood due to concern that visitors to the United Kingdom and Europe could have been exposed to mad cow disease.

Although researchers do not know whether the agent that causes the fatal degenerative brain disease can actually be transmitted through blood, the agency said it wants to limit the theoretical risk that blood recipients could face.

"We are taking these steps to help protect the safety of the blood supply at a time when science does not allow us to rule out the risk of transmission of [mad cow disease] through blood transfusions," said Bernard A. Schwetz, acting head of the FDA.

The limits on blood donations are primarily directed at Americans who lived in the United Kingdom, where most of the approximately 100 known cases of the disease have been diagnosed. Under the new guidelines, which the FDA wants to impose by May 31, 2002, people who stayed there for three months or longer between 1980 and 1996 would not be able to donate blood.

Because three cases of mad cow disease have recently been found in France, the FDA wants to impose blood donation restrictions on people who stayed there for more than a total of five years since 1980. Under the FDA plan, the restrictions would expand by November 2002 to include all who stayed for five years anywhere in Europe since 1980.

Currently, blood donations are banned only from people who stayed in the United Kingdom for more than six months between 1980 and 1996.

While the number of cases of mad cow disease in humans remains low, thousands of animals in the United Kingdom and, more recently, Europe have been destroyed because they tested positive for the disease, which is also known as bovine spongiform encephalopathy.

Researchers have established that humans can develop the disease after eating infected beef, although they do not know exactly how the disease spreads.

The FDA proposal would also ban blood donations from U.S. military personnel stationed in northern Europe during the 1980s, and those living in southern Europe until 1996. The FDA concluded that soldiers and their families on military bases may have eaten British beef during that time period.

The proposed rules are not as strict as those that the American Red Cross plans to implement next month. The organization, which collects half of the nation's blood supply, will refuse donations from anyone who has spent three months in the United Kingdom or six months anywhere in Europe since 1980. Some suppliers of blood products have voiced concern that the Red Cross and FDA restrictions could cause shortages in some areas.

Mad cow disease is a variant of the rare brain disease called Creutzfeldt-Jakob disease (CJD). While CJD is present in the United States, there have been no confirmed reports of the mad cow version outside of Europe.

Jay Epstein, director of the FDA's Office of Blood Research and Review, said that 95 percent of people eligible to donate blood would remain eligible under the proposed new rules. But he said that 90 percent of the risk of mad cow transmission through blood would be eliminated by the changes.

The FDA plans to issue its final regulations on blood donations by the end of the year.

Washington Post August 28, 2001; Page A08