The cattle will be barred from the human food supply, even though they ate a very small amount of the feed and the risk of a mad cow outbreak is small.
While there has been no sign of the disease in the United States, mad cow disease has killed more than 80 people, mostly in Britain, with a few in France, Ireland and elsewhere in Europe.
CBS News Health Contributor Dr. Bernadine Healy, who is also the president of the American Red Cross, spoke about it on The Saturday Early Show.
Here are her answers to some questions about mad cow disease:
- What is mad cow disease and how did it start?
Mad cow disease, also known as bovine spongiform encephalopathy, is a fatal condition that affects the nervous system. In an affected animal, the brain develops tiny holes, making the animal lose control over its movements and changing its behavior. Mad cow disease spread in British herds in the mid-1980s after they were fed the processed animal remains of sheep infected with scrapie, a closely related brain-wasting disease.
- Is mad cow disease a virus or bacteria?
It's neither. Mad cow disease is in a new class of infectious agents called prions. The disease is caused when a normal prion protein folds into an abnormal shape and no longer breaks down inside the body. Such misfolded proteins produce havoc in nervous tissue, often leaving sponge-like holes in many parts of the brain.
When an animal or person eats or is exposed to tissues containing abnormal prions, their own prion proteins are converted into the deadly abnormal form.
Prions can also misfold on their own accord and give rise to disease. Occasionally, genetic mutations lead to prion diseases that run in families. Mad cow disease has jumped species - from sheep to cows to humans.
- How do humans contract mad cow disease?
It's believed that mad cow disease is spread to people when they eat infected beef products. The human version is known asa new variant Creutzfeldt-Jakob (vCJD) disease to distinguish it from a form of CJD that occurs naturally in about one in a million people. Since the first human cases were diagnosed in 1996, more than 80 people have died of vCJD in Britain and three in France.
- What are the symptoms in humans and when do they show up?
New variant CJD begins with psychiatric symptoms such as anxiety and depression. It then progresses with premature dementia, loss of motor control and early death. Experts still do not know how extensively the disease will spread, because it can take years or even decades to show symptoms. There is an incubation period of 5 to 10 years before we see the symptoms. Unfortunately at this time, we still do not have a treatment for vCJD.
- How great is the risk of contractig the human form of mad cow disease?
The risk is unknown, but many scientists believe vCJD will remain a very rare disease. Keep in mind that there are a lot of things we don't know about the disease, so many of the unknown variables could change any predictions. Until we develop a test such as a blood test, we won't know if this disease is a big or small problem. We estimate that such a blood test is two or three years away.
- Are certain cuts of meat more dangerous than others?
It's believed that the infectious agent suspected of being the cause of the disease (prion protein) is found in brain and spinal cord tissue. This material could accidentally be mixed with meat in ground beef, sausages, and other foods. Some hamburgers and sausages may contain up to 20 percent brain tissue. Some scientists even speculate that it got into pureed meats used in baby foods in the U.K. Muscle tissue such as steaks and roasts are thought to be free of infection, as are dairy products.
- What is being done to protect our food supply?
As far as anyone can tell, the U.S. food supply is safe. There has been ongoing surveillance of cattle to look for evidence of mad cow disease. So far, USDA scientists have examined the brains of nearly 12,000 cattle suspected of having brain impairment and found no hint of the disease.
Since 1989, the USDA has banned the import of cattle from BSE-infected countries. And, in 1997, the FDA prohibited the use of most cow remains in cattle feed.
The goal is to avoid the practice of feeding cows back to cows, which is thought to have caused the explosion of BSE in Europe. Last month, an FDA advisory panel recommended expanding a blood donation ban for people who have spent time in the U.K. to include those who had lived in France, Portugal or Ireland for 10 years or more since 1980.
- Should we stop eating beef?
We are told that our beef is safe, and we should have faith in our government that they are monitoring our food supply. So far, there is no evidence of mad cow disease in the U.S. However, everyone should be aware of this disease and keep an eye on developments.
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