Brain & Nervous System Health Center

Mad Cow Disease May Be Transmitted Before Symptoms Appear

From the WebMD Archives

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.


Bostock says he does not believe additional precautions need to be taken to safeguard the blood supply as a result of his findings. But he says they confirm the earlier measures, including the ban on U.S. blood donations from certain people.


Paul Brown, PhD, of the laboratory of Central Nervous System Studies, under the National Institutes of Health, tells WebMD he does not think these early results from the British research should have been published. He wrote a commentary accompanying the research paper.


"It doesn't change our fundamental way of thinking about this disease," Brown says. "Transfusion has been used for transmission and we know that the blood is infectious. It doesn't change a thing" in terms of the precautions required for blood donations.


For him, the study's message is limited to its finding that mad cow disease can be transmitted during the disease's incubation period in an "experimental model" involving a blood transfusion from one sheep to another. This does not imply that a sheep could give the disease to a lamb, or that one sheep could naturally transmit it to another even though it shows no symptoms, Brown says.


Bostock tells WebMD that he wanted to publish his early results because he believed they were in the public interest.


"The fact is, this experiment in its entirety would take 10 years to complete," Bostock says. "If we were to keep the work secret, that we had a positive transmission, we would be in an extremely uncomfortable position.


"We are also investigating whether [mad cow disease] can be transmitted between individuals -- either mother to lamb or sheep to sheep," Bostock adds.


Roger Dodd, PhD, head of transmissible research at the Jerome Holland Laboratory in Rockville, Md. -- the primary research facility for the American Red Cross -- tells WebMD that the researchers' finding confirms expectations. The fact that the sheep developed mad cow disease during the disease's incubation period was the reason "precautions were put in place" for blood donations, he notes.



The researchers say that developing a test to diagnose mad cow disease is among the most important steps in combating the disorder. In the early 1980s, when little was known about the cause and transmission of AIDS, the world's blood supply was unprotected against HIV, and some people developed the disease from transfusions with infected blood. Now tests are run to screen blood for HIV, but screening of donors is the primary way the blood supply is guarded today.


Brown calls the association between HIV and mad cow "unwise," saying the two diseases "are so different." But Bostock acknowledges that the situation is similar to the days when no tests were available to detect HIV in the blood supply. Even today, with advanced testing available to detect HIV, there is a two-week window between the time a person is infected with HIV and when the disease can be detected in the blood.


Brown tells WebMD he believes the U.S. will be spared outbreaks of mad cow disease. "There are lots of embargoes and lots of prevention. I think we have escaped and will continue to escape."

WebMD Health News Reviewed by Annie Finnegan on September 14, 2000
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