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Regulators Debate U.S. Response to Mad Cow Disease

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In this case, there are some striking similarities. "We simply don't know if there is the potential for CJD to be in the blood of donors," explains Steve Petteway, director of pathogen safety and research at Bayer Corp., where groundbreaking work has been done on that subject. But studies have shown that the infectious agent may reside in the blood of animals, which lends credibility to the FDA's concern, he says.

To find the answer, scientists around the world are working on a test to detect an unconventional protein called a prion, a previously unknown infectious agent believed to be behind CJD. Prions are thought to transform healthy molecules to a dangerous conformation, causing not only CJD but also mink encephalopathy, scarpie in goats and sheep, chronic wasting disease of mule deer and elk, feline spongiform encephalopathy, and bovine spongiform encephalopathy -- or mad cow disease.

Experiments with mice in which scientists managed to transfer CJD using prions show there is good reason to believe that prions are the cause of the disease, says Mary Jo Schmerr, PhD, the lead scientist for prion diseases at the National Animal Disease Center, a division of the USDA.

Based on that data, Schmerr has developed a test for animals and is now working on a test to extract prions from concentrated human blood samples. Such a test, she tells WebMD, would go along way toward detecting the disease in its early stages, when treatment might still be possible.

Based on that data, others also are working on a test to confirm whether their methods for extracting matter from the lining of the human brain and for extracting blood components reduces the risk of inadvertently transferring the disease from an infected person to a healthy person. So far, that work has demonstrated the value of using animal models, and that once the prions are removed, the disease cannot be transferred, Petteway tells WebMD.

But at least one researcher who has studied CJD for 25 years still is disputing the official version of what causes CJD, and if he is right, researchers may not be able to develop a reliable early screening test. Also at question is whether government regulators can accurately assess the risk posed by CJD, which some say may be far more prevalent than originally thought.

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