Brain & Nervous System Health Center

The Basics of Mad Cow Disease

Mad cow disease has hit the U.S. and questions about this mysterious disease abound. Here's what you need to know about mad cow disease.

What Is Mad Cow Disease?

Mad cow disease, or bovine spongiform encephalopathy (BSE), is a transmissible, slowly progressive, degenerative, and fatal disease affecting the central nervous system of adult cattle. The U.S. Department of Agriculture (USDA) has tested hundreds of thousands of cattle for BSE.

Researchers believe that the infectious agent that causes mad cow disease is an abnormal version of a protein normally found on cell surfaces, called a prion. For reasons still unknown, this protein becomes altered and destroys nervous system tissue -- the brain and spinal cord.

Does Cooking Food Kill the Prion That Causes Mad Cow Disease?

Common methods to eliminate disease-causing organisms in food, like heat, do not affect prions. Also, prions only seem to live in nervous system tissue.

Does Mad Cow Disease Affect Humans?

A human version of mad cow disease called variant Creutzfeldt-Jakob disease (vCJD) is believed to be caused by eating beef products contaminated with central nervous system tissue, such as brain and spinal cord, from cattle infected with mad cow disease. For this reason, the USDA requires that all brain and spinal cord materials be removed from high-risk cattle -- older cattle, animals that are unable to walk, and any animal that shows any signs of a neurological problem. These cow products do not enter the U.S. food supply. The USDA believes this practice effectively safeguards U.S. public health from vCJD.

According to the CDC, four deaths from vCJD have been identified in the U.S. However, it's believed those cases were caused by consumption of meat outside the U.S.

It is important to clarify the differences between variant CJD and another form of the disease, referred to as classic or sporadic CJD. Classic CJD has no known cause and occurs each year at a rate of one to two cases per 1 million people throughout the world, including in the U.S. and countries where mad cow disease has never occurred. It is not linked to eating nerve tissue from mad cow disease-affected cattle -- both vegetarians and meat eaters have died from classic CJD. CJD most commonly affects people over 65 and is usually fatal within six months from onset of symptoms.

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What Are the Symptoms of vCJD?

The disease can affect all age groups and is very hard to diagnose until it has nearly run its course. In the early stages of vCJD, people have symptoms related to the nervous system, like depression and loss of coordination. Later in the illness, dementia develops. But only in advanced stages of the disease can brain abnormalities be detected by MRI (magnetic resonance imaging). vCJD is fatal, usually within 13 months of the onset of symptoms.

Is it Possible to Get vCJD From Eating Food Purchased in the U.S.?

It is extremely unlikely that this would happen. To prevent mad cow disease from entering the country, since 1989 the federal government has prohibited the importation of certain types of live animals from countries where mad cow disease is known to exist. This ban includes meat products used in human, animal, and pet foods. In addition, prohibiting high-risk animals from entering the food supply and the removal of central nervous system tissue from the food supply helps assures that BSE is not a risk to consumers.

Can You Get vCJD From Drinking Milk From an Infected Cow?

Milk and milk products are not believed to pose any risk for transmitting mad cow disease to humans. Experiments have shown that milk from mad cow-infected cows has not caused infections.

What About Other Products Made From Cow By-Products?

The FDA stops the importation of cosmetic and dietary supplement ingredients containing bovine materials from animals originating in the 33 countries where mad cow disease has been found or from animals at risk of being infected.

What Is the Current Risk of vCJD to Americans Traveling Abroad?

According to the CDC, the current risk of acquiring vCJD from any specific country appears to be extremely small. But that cannot be precisely determined because cattle products from one country might be distributed and consumed in others.

How Long Have Health Officials Been Concerned About Mad Cow Disease?

Mad cow disease has been of great concern since 1986, when it was first reported among cattle in the U.K. At its peak in January 1993, almost 1,000 new cases per week were identified. Concern about this disease grew significantly in 1996 when an association between mad cow disease and vCJD in humans was discovered.

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What Other Countries Have Reported Cases of Mad Cow Disease?

The disease also has been confirmed in cattle born in Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Italy, Ireland, Israel, Japan, Liechtenstein, Luxembourg, the Netherlands, Poland, Portugal, Slovakia, Slovenia, Spain, Switzerland, and the U.K.

Canada has also been added to the list of countries from which imports are restricted, although that ban has been lifted recently. Importation of minimal-risk meat products is now allowed from Canada.

WebMD Medical Reference Reviewed by Neil Lava, MD on June 12, 2016

Sources

SOURCES: USDA. CDC. FDA.

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