And apparently, contrary to strong assertions from the cattle industry and the government, there is some doubt as to how Mad Cow is transmitted.
denverpost.com
Article Published: Sunday, December 28, 2003
Single case unlikely to spur blood donation restrictions
By Diedtra Henderson
Denver Post Science Writer
In the face of 180,000 sick cattle in the United Kingdom and a growing number of people suffering from the human equivalent of mad cow disease, American authorities barred blood donations from people who had spent months in the U.K. during that epidemic.
A single case of mad cow confirmed this month in Washington state is unlikely to prompt a repeat of those aggressive protection measures. The risk of mad cow-tainted blood seeping into the nation's supply from American donors is minimal, officials said. And, for now, there's no practical way to exclude suspect donors without reducing blood donations to a trickle.
"I don't see how a donor-deferral criteria could be applied to the U.S.,' said Dr. Kenrad Nelson, a Johns Hopkins University professor who chairs the Food and Drug Administration's Blood Products Advisory Committee. "The way beef is transported and mixed with other beef, there's probably no way they can even trace the meat from that one animal. ... You can't assume it was consumed in Washington state. It could be New York. Or Maryland. Or Denver.'
The American Red Cross, which supplies nearly half of the nation's blood, had no comment on excluding Washington state blood donors, said spokeswoman Lesly Hallman. The agency intends to "follow the guidance of the FDA,' according to a statement on its website.
That federal guidance is unlikely to come unless a mad cow epidemic occurs in Washington or there's firm confirmation the fatal disorder can be spread by blood donations, said Dr. Harvey Klein, chief of the department of transfusion medicine at Warren G. Magnuson Clinical Center in Maryland.
"I think that it is too early for any kind of conclusions about the need to change policy,' agreed FDA spokeswoman Lenore Gelb. "Certainly, we have strong measures in place to protect the blood supply.'
The FDA uses donor exclusions to help prevent the spread of blood-borne pathogens for which diagnostic tests don't exist or don't work reliably in blood. For example, at least 18 percent of military personnel - normally reliable and repeat blood donors - cannot donate because of possible mad cow exposure during past assignments to European bases. And troops returning from Iraq will face a one-year waiting period before donating blood for fear they were exposed to a parasitic disease spread by sand flies.
Lab workers confirm mad cow infections by testing tissues that are chock-full of the highest concentrations of abnormally folded, disease-causing prion proteins. Getting brain and spinal cord samples from slaughtered cattle is relatively easy.
"It would be hard to screen blood donors by doing a tonsil biopsy,' Nelson said. "That just isn't going to work.'
Variant Creutzfeldt-Jakob disease (vCJD) is thought to have spread to humans who ate mad-cow tainted meat products. But United Kingdom Health Secretary John Reid this month said the government is investigating a possible case of human infection through blood transfusion.
A blood donor developed vCJD two years after the 1997 donation. Six years later, in 2003, one transfusion recipient also developed the debilitating and always-fatal brain disease. That individual died earlier this month. If confirmed, it would be the first person-to-person transmission of the rare neurological disease.
"It seems to me almost certainly this was transmitted by the blood rather than through food,' Nelson said. "My guess is the risk of variant Creutzfeldt-Jakob disease transmitted by blood is quite small, but it may not be zero.'
A second person received blood from the same donor. And 14 others received blood from U.K. donors who later developed vCJD. Those individuals have not shown signs of infection. But the disease can silently incubate for years, causing death shortly after symptoms are apparent.
Despite that ongoing investigation, Klein, another FDA Blood Products Advisory Committee member, said the risk of passing mad cow through tainted blood donations "is still hypothetical.'
"Residents of the U.K. were never excluded in the U.K. (nor were butchers, farmers, etc.) Despite that fact, no evidence of blood transmission has emerged,' he said.
Denver Post science writer Diedtra Henderson can be reached at dhenderson@denverpost.com or 303-820-1910. |
