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Mad Cow Disease May Be Transmitted Before Symptoms Appear

WebMD Health News
Reviewed by Annie Finnegan

Sept. 14, 2000 -- While no cases of "mad cow disease" have been discovered in the U.S., officials here have taken precautions to ensure that our blood supply is safe from this potentially fatal illness. And new research indicates it was smart to take such steps.


Researchers in England have documented the first case of an animal developing mad cow disease after getting a blood transfusion from a sheep that had been exposed to the disease but did not yet appear to be sick. The donor sheep also later developed the disease.


While a top U.S. official played down the importance of this event, the study's author tells WebMD it shows that the disease can be transmitted through blood before an animal appears ill.


The official name of mad cow disease is bovine spongiform encephalopathy (BSE), so named because the brains of the affected animals actually develop holes, like sponges. People who ate beef from cattle that had mad cow disease have developed a disorder called new variant Creutzfeldt-Jakob disease, a rare but fatal neurological condition.


As of Sept. 5, officials in the U.K. have reported 82 cases of the neurological disease. Mad cow disease is epidemic in cattle there. No cases of the neurological disorder, nor of mad cow disease, have been seen in the U.S.


Currently, there is no way to test for the presence of mad cow disease in blood, and some even debate whether the disorder can be transmitted by blood. But under orders from the FDA, the American Red Cross no longer accepts blood donations from people who spent a total of six months or more in England, Northern Ireland, Scotland, Wales, Isle of Man, or the Channel Islands between 1986 and 1996. These rules were put in place in August of 1999.


In the U.K., the blood goes through a special process to remove infections, and officials there import plasma and plasma products from countries that have no BSE cases.


The new report, published in the British journal Lancet, was written by Chris Bostock, PhD, and other staff of the Institute for Animal Health in Berkshire, England. The authors fed tissue from cattle that had mad cow disease to healthy sheep, took blood from those sheep while they were still seemingly healthy, then transfused the blood into other healthy sheep. One sheep developed mad cow disease after it got the blood transfusion, and so did the sheep from which the blood was taken.


The authors calculate that, based on when sheep ate the contaminated cattle tissue, the sheep must have been able to pass on the disease before it started showing symptoms -- something that has been suspected but never before proven.

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