Mad cow disease seems to pop up in the news now and then. But what is it, and how likely is it that people will get it?

What Is Mad Cow Disease and How Do People Get It?

Mad cow disease is an incurable, fatal brain disease that affects cattle and possibly some other animals, such as goats and sheep. The medical name for mad cow disease is bovine spongiform encephalopathy (pronounced: bo-vine spun-jih-form en-seh-fah-la-puh-thee), or BSE for short. It's called mad cow disease because it affects a cow's nervous system, causing a cow to act strangely and lose control of its ability to do normal things, such as walk.

Only certain animals can get BSE — people don't actually get mad cow disease. However, experts have found a link between BSE and a rare brain condition that affects people, called variant Creutzfeldt-Jakob disease (CJD). Researchers believe that people who eat beef from cows that have BSE are at risk of developing a form of CJD.

CJD is caused by an abnormal type of protein in the brain called a prion. When people have CJD, cells in the brain die until the brain eventually has a "sponge-like" appearance. During this time, people with the disease gradually lose control of their mental and physical capabilities.

To date, very few people have been diagnosed with the form of CJD that's been linked to mad cow disease. By November 2006, only 200 cases of this rare condition had been reported worldwide. Of these, most were identified in Britain. Several of the people diagnosed with the disease outside Britain — including two cases in the United States — had a history of exposure in Britain or in a country where government officials reported BSE. Experts believe that the people got CJD after eating beef products from cows that had BSE.

Because the form of CJD that's been linked to mad cow disease is relatively new and extremely rare, experts are still learning about it. However, researchers believe that the disease is not contagious among people. In other words, you cannot get CJD from someone else who has it. At present, it appears that the main way people get the disease is from eating contaminated meat.

Experts don't yet know exactly how long the incubation period is for CJD (in other words, how long it takes from the time a person contracts it to the time that symptoms first appear). However, they do believe that it takes years, if not decades, from the time someone is exposed to the disease until the first signs appear. After the first signs appear, the brain can deteriorate within a year.

What's Being Done?

If you're worried about mad cow disease, tell whoever buys the food in your household about how you feel. The type of protein that causes mad cow disease cannot be removed or destroyed when beef is processed or cooked. For this reason, the U.S. government has established several meat processing procedures to protect the public. One of these steps involves removing the parts of the cow that are at highest risk of containing BSE-causing proteins — the brain and spinal cord — to reduce the chances of them contaminating the meat people eat.

In October 2005, the U.S. Food and Drug Administration (FDA) proposed additional safeguards to help protect consumers from BSE. These prohibit the use of any high-risk cattle materials in the feed of any animal. In this way, the FDA continues to decrease the already tiny possibility of infection with BSE.

There is also a system in place to test samples of meat regularly. The testing system helped officials identify some contaminated meat in Washington state in December 2003 — one of only three cases of mad cow disease found in the United States so far.

The government has a recall policy for meat that's suspected of being contaminated. This helps prevent contaminated meat from reaching the shelves.

If you're wondering if you can get sick from drinking cow's milk, rest assured that you can't. The United States Department of Agriculture (USDA) says there is no evidence that the disease is transmitted through cow's milk and milk products.

The good news is that it's highly unlikely that a person will contract CJD from eating beef. CJD itself is pretty rare. And because only three cows in the United States have been found to be infected with mad cow disease, which can't be spread from cow to cow, the chance that you will eat meat infected with the disease is extremely low.

Reviewed by: Larissa Hirsch, MD
Date reviewed: January 2007
Originally reviewed by: Steven Dowshen, MD