Mad Cow Disease

Overview

What is mad cow disease?

Mad cow disease is a fatal neurological disease that slowly destroys the brain and spinal cord (central nervous system) of cattle. It also is known as bovine spongiform encephalopathy, or BSE.

Can people get mad cow disease?

People cannot get mad cow disease. But in rare cases they may get a human form of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD) if they eat nerve tissue (the brain and spinal cord) of cattle that were infected with mad cow disease. Variant Creutzfeldt-Jakob disease is a fatal condition that destroys the brain and spinal cord.

There is no evidence that people can get mad cow disease from eating muscle meat—which is used for ground beef, roasts, and steaks—or from consuming milk or milk products. People who develop vCJD cannot spread the disease to other people through casual contact.

As of November 2006, 200 human cases of vCJD had been reported in the world: 164 from the United Kingdom, 21 from France, 4 from Ireland, 3 from the United States, 2 from the Netherlands, and 1 each from Canada, Italy, Japan, Portugal, Saudi Arabia, and Spain. Two of the three people in the United States, two of the four people in Ireland, and the people from Canada and Japan all visited or lived in the United Kingdom when they became infected. One of the people with vCJD in France may also have been infected in the United Kingdom.¹

To help protect people from getting vCJD, people who have visited or lived for three months or more in specific countries such as the United Kingdom or France between 1980 and 1996 are not allowed to donate blood in the United States or Canada.^{2, 3}

What causes mad cow disease and variant Creutzfeldt-Jakob disease (vCJD)?

No one is sure what causes mad cow disease. One theory is that the disease is caused by a change in the shape of some of the proteins found in animal cells. This change may be caused by other abnormal proteins called prions. In affected cows, the abnormal proteins (prions) are found in the brain, spinal cord, and small intestine. There is no evidence that these abnormal proteins are found in muscle meat (such as steak) or in milk. Another theory is that mad cow disease is caused by a virus that causes the proteins to change and become abnormal (prions).⁴

When a cow is slaughtered, certain parts of it are used for human food and other parts are processed into animal feed. If an infected cow is slaughtered and its nerve tissue is used in cattle feed, other cows can become infected. In rare cases, people can develop vCJD if they eat the brain or spinal cord tissue of infected cattle.

In December 2003, mad cow disease was discovered in one cow in the United States. Before this cow was identified as having the disease, the cow was slaughtered and its muscle meat entered the human food supply. Its organs or nerve tissue were not used for human food. Although BSE cannot be spread through muscle meat, the United States Department of Agriculture (USDA) quickly traced the meat and pulled it from grocery stores.

Between 2004 and 2006, only two more cows in the United States were found to have mad cow disease. But these two cases were different from the first case found in the United States and the results were not typical of mad cow disease. There is some disagreement about whether these two cases were really mad cow disease at all.

What are the symptoms of vCJD?

Variant Creutzfeldt-Jakob disease (vCJD) causes the brain to deteriorate, and it is eventually fatal. Symptoms include:

• Tingling, burning, or prickling of the face, hands, feet, and legs. But there are much more common illnesses with these same symptoms. Having tingling in your hands or feet does not mean you have vCJD.
• Dementia.
• Psychotic behavior.
• Coordination problems. As the disease progresses, a person is no longer able to walk.
• Coma.

If a person does eat prions from an infected cow, he or she may not feel sick right away.The incubation period—the time from exposure to the disease until symptoms develop—is not fully known, but experts think it is years.

How is vCJD diagnosed?

There is no single test to diagnose variant Creutzfeldt-Jakob disease (vCJD). Doctors may suspect that a person has vCJD based on symptoms, medical history, and a review of where the person has lived. Imaging tests, such as an MRI, may be done to check for brain changes caused by vCJD.

Researchers currently are trying to develop a blood test that detects vCJD. But no blood test is available at this time.

A brain biopsy is the only way to confirm a diagnosis of vCJD.

How is vCJD treated?

There is no cure for vCJD. Treatment includes managing the symptoms that develop as the disease progresses.

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Author:	Monica Rhodes	Last Updated April 23, 2007
Medical Review:	Wajeeh E. Nasser, MD - Family Medicine W. David Colby, MSc, MD, FRCPC - Infectious Disease
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