Mad Cow Disease

What is this illness called ‘mad cow’ disease?

The illness got its name because cows afflicted with it stumble around as if they’ve lost their balance. They act demented (or “mad,” as the British say) and quickly die of the disease. The cows actually have a fast-moving, irreversible brain disease. They are infected with bovine spongiform encephalopathy (BSE), a degenerative central nervous system disease that affects the brains of cattle, killing brain cells and creating spongy holes in the tissue.

BSE, commonly known as “mad cow disease,” belongs to a family of debilitating brain diseases that can affect other animals bred for human consumption. And when humans eat boned meat and organs from these infected animals, they risk becoming infected as well. As in cows, the illness is invariably fatal.

Fortunately, mad cow disease is extremely rare in the United States. According to the Centers for Disease Control and Prevention (CDC), as of 2009, there have only been three reported cases in people in the United States, and there is strong evidence that all three were exposed to BSE outside the United States.

Most of the reported cases around the world are from Great Britain, where an outbreak of BSE occurred between 1980 and 1996. Between 1994 and 1996, a dozen people between the ages of 19 and 39 came down with what seemed to be Creutzfeldt-Jakob Disease (CJD), another brain disorder. Scientists later found that the victims’ brains looked more like the brain of a cow infected with BSE than that of a person with classic CJD. Scientists eventually called the disease “new variant Creutzfeldt-Jakob disease” (vCJD).

What causes BSE and vCJD?

Scientists are still debating the cause of the disease. Researchers believe there are two strains of BSE: a classic or “typical” one found in Canada and the United Kingdom, and an “atypical” one found in the U.S., which may have developed independently of the strain found elsewhere. Some researchers initially suspected a virus, but most now believe that this family of brain diseases is caused by so-called “renegade” proteins called prions. These abnormal prions enter brain cells and turn healthy proteins into a lethal form that damages brain cells and causes them to die.

It’s likely that BSE was spread among cattle through the food that cows eat. Until 1997, it was common to supplement cattle feed with meat and bone meal made from animal carcasses, including sheep and other cows. Some experts speculate that this practice enabled a form of the disease found in sheep to make the jump to cows, causing BSE.

Once the prions from an infected cow get into the digestive system of a healthy cow, they can spread to the nervous system and cause BSE. Researchers believe that these proteins, when consumed by other animal species, can jump the species barrier. Likewise, scientists believe that prions can cause vCJD in people who eat animal organs infected with BSE.

How likely is an outbreak in the United States?

Not very likely, but government officials haven’t ruled out the possibility. Although some experts contend it is only a matter of time before the disease appears in the United States, a Harvard study concluded that “BSE is extremely unlikely to become established in the U.S.”

Still, federal officials are wary, given recent threats. There have been three cases of BSE identified in cows in the United States (in 2003, 2004, and 2006). The 2003 case involved a cow born in Canada, where it presumably caught the disease before being imported into the United States. The 2004 case was the first endemic case of BSE in the U.S., and officials have not been able to determine the origin of the cow diagnosed in 2006. There have been 18 cases of BSE in Canada, with the latest one reported in February 2010.

To prevent the risk of contamination, the USDA has banned the import of meat and meat products from Britain, as well as cattle feed made from cows and other livestock. But the discovery of mad cow disease in the United States triggered a chain of new reforms geared to make beef even safer. The U.S. Department of Agriculture banned cows that can’t walk (also known as “downer cows”) for human consumption. The agency also prohibited the sale of brains and spinal cord tissue — the organs most likely to be contaminated — from cattle 30 months old or older.

In March 2004, the USDA also ramped up its surveillance program. Between 2004 and 2006, over 750,000 cows were sampled. Since then, the agency has determined that the prevalence of BSE in cows in the United States is extremely low (less than one cow per million adult cattle). As a result, its surveillance program now samples about 40,000 cows per year.

Are there precautions I can take?

Although the CDC estimates the risk of acquiring vCJD through eating beef to be very low — at the most, about one case per 10 billion servings (in the UK, where the largest number of cases have been reported) — taking some precautions can help to ease your fears. Experts at the Center for Science in the Public Interest (CSPI) suggest choosing cuts of meat and products that are less likely to be infected with the disease. Products with no known risk include cuts of boneless beef, beef from grass-fed cattle, and all dairy products.

Cuts of beef containing a bone, such as prime rib, porterhouse and T-bone steaks, and rib roasts carry what the CSPI describes as a “minuscule” risk. Potentially riskier products include beef sausages, hot dogs, pizza toppings, and hamburger meats in which different cuts of beef are mixed together. The most risky products are those that contain brains and the spinal cord.

Although swearing off beef is unnecessary, you might want to take a few precautionary steps anyway.


Centers for Disease Control and Prevention. BSE (Bovine Spongiform Encephalopathy, or Mad Cow Disease). August 26, 2010.

Centers for Disease Control and Prevention. Fact sheet: New variant Creutzfeldt-Jakob disease. August 23, 2010.

Centers for Disease Control and Prevention. Questions and answers regarding bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease (CJD). August 26, 2010.

U.S. Food and Drug Administration. Commonly asked questions about BSE in products regulated by FDA’s Center for Food Safety and Applied Nutrition (CFSCAN).

United States Department of Agriculture. Bovine spongiform encephalopathy.

Federal Department of Agriculture. Questions and answers on bovine spongiform encephalopathy.

National Institutes of Health. Prions: puzzling infectious proteins.

U.S.: Mad cow meat recall 4 times larger. March 2, 2004. Ira Dreyfuss, Associated Press.

Center for Science in the Public Interest. Choosing safer beef to eat. January 6, 2004.

Centers for Disease Control and Prevention. Travelers’ health: bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease.

USDA. USDA Announces New BSE Surveillance Program. July 20, 2006.

Spongiform Encephalopathy Advisory Committee. Position Statement: New Forms. July 2007.

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