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.