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Beware the Shapeshifter:
The blood threat

by Alicia P. Gregory

"The safety of the blood supply is an important issue," says Telling. "The very limited experiments that have been done suggest that if there is any infectivity in blood, it's at relatively low levels. But a new strain may arise that accumulates prions at much higher levels in blood. It's an open question whether new variant CJD could cause that sort of a problem."

In June 2002, the U.S. Food and Drug Administration permanently banned the following groups from giving blood: anyone who lived in the U.K. for three months or more, and personnel and their families stationed at military bases in Europe for six months or more from 1980 to 1996; anyone who lived in France for five years or more, and anyone who received a blood transfusion in the U.K. since 1980.

In November 2002, scientists at Britain's Institute of Animal Health published data in the Journal of General Virology that leads to the alarming conclusion that people may be more likely to contract CJD through blood transfusions than originally thought. The ongoing study of 24 sheep found that two contracted BSE after being transfused with blood from infected sheep, and two more developed clinical signs of the disease. If the later two sheep do develop BSE, the transmission rate would be 17 percent.

Previous work suggested that in BSE, and by extension new variant CJD, infectivity is concentrated in the white blood cells. Based on this, blood donated in the U.K. is filtered to remove white blood cells. But in this new study, which transfused whole blood and white blood cells only, none of the sheep transfused with the white blood cells developed the disease. The two confirmed and two suspected cases are both among the 17 sheep that received one unit of whole blood. This indicates plasma and red blood cells may have a greater infectivity potential than previously thought.

Another disturbing finding, based on post-mortem studies of the sheep, indicates that prions transmitted through blood transfusions do not spread through the body in the same way as prions transmitted through eating infected meat. These sheep had far less prion build-up in their tonsils—tonsil biopsies are the primary test now given to humans who may have been infected by transfusions, so a negative biopsy may not be reliable.

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