Mad Cow Disease May Be Transmitted Before Symptoms Appear
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
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.