sealPurdue News

December 1999

Mad cow disease in the United States

Although no cases of mad cow disease have been found in humans or livestock in the United States, according to a Purdue expert, recent news articles have suggested that individuals have died from the disease. Although there is no scientific confirmation of these reports, they have nonetheless had an impact.

After an article appeared nationally in April 1997, suggesting that a 62-year-old Schererville, Ind., man died of mad cow disease, cattle options traded on the Chicago Mercantile Exchange fell the maximum allowed for one day's trading, and corn and wheat futures fell as well. The next day (4/18), the Purdue Agricultural Communication office received a phone call from a radio station in Kokomo, Ind., asking for information because a local grocer was pulling milk off the shelves.

In October 1999 another news article in Indiana suggested that a man had died of mad cow disease. There has been no scientific confirmation of that claim.

Here is basic information about mad cow disease and its occurrence in the United States:

What is mad cow disease?

According to Leon Thacker, director of the Animal Disease Diagnostic Laboratory at Purdue University, mad cow disease is a popular term given to a disease of cattle known as bovine spongiform encephalopathy, or BSE. There have been more than 176,000 cases in cattle worldwide since the disease was first discovered in Great Britain in 1986, and 95 percent of the cases have been in the United Kingdom.

In humans, a very similar disease called Creutzfeldt-Jakob causes slow degeneration of the brain. It is believed that mad cow disease in humans is a new variant of that disease.

How common is mad cow disease in the United States?

The reported incidence of classic Creutzfeldt-Jakob disease is one case per million people. From this, experts predict that approximately 270 people per year will die in the United States from the disease. Worldwide, there have been 40 confirmed cases in the past 13 years of people dying from the new variant of Creutzfeldt-Jakob disease that causes mad cow disease. Some scientists suspect that those people acquired the disease by eating beef from infected cattle, but the method of infection remains unclear.

Because of the widespread media attention this disease has received, prompted in part by the curious name it has been given, many people assume that the disease has appeared in this country. But according to Thacker, there have been no known cases of mad cow disease in the United States in either humans or livestock. "That is one of the things we all need to keep in mind as we look into these cases," Thacker says.

What causes mad cow disease?

Most scientists believe that BSE is caused by a small agent called a prion. A prion is neither a virus nor a bacterium, but instead is an infectious protein. There are some scientists who say that because the prion does not contain its own genetic material it cannot be an infectious agent. Stanley Prusiner of the University of California, who first developed the theory of the prion as an infectious agent, received a Nobel Prize for his work in 1997.

The cause of Creutzfeldt-Jakob disease is unknown, but there is some indication that heredity plays a part.

How would you tell if a person died from mad cow disease?

At present, the diagnosis of BSE or Creutzfeldt-Jakob disease can only be made on a cow or human after death. The definitive diagnosis is made by looking at changes in the brain or identifying the specific prion protein in the affected cow or human brain tissue.

However, there is a medical indication that provides a clue to whether BSE or Creutzfeldt-Jakob was involved. Classic Creutzfeldt-Jakob affects people of an average age of 65, but the average age of people who died from BSE is 27.5. In fact, it was this unusual age difference that first caused medical scientists in Europe to investigate the deaths that were eventually diagnosed as BSE.

"Just the fact that the person who died is 68 years old would be enough to give me pause," Thacker says. "That's not enough reason to dismiss the possibility that someone may have died from BSE, but it sure puts some doubt in my mind."

Where can I get more information on mad cow disease?

The Purdue Cooperative Extension Service has recently published "Mad Cow Disease: Is It a Threat to the U.S. Food Supply?" a publication that is available on the Internet.

Other related Web sites:
World Health Organization fact sheet on BSE
University of Illinois BSE Web site
USDA BSE Web site
FDA BSE Web site
"The Prion Diseases," Stanley Prusiner, Scientific American, Jan. 1995:
New Scientist articles on BSE
PBS documentary "The Brain Eater":

Leon Thacker, director
Purdue Animal Disease and Diagnostic Laboratory
(765) 494-7460

Steve Tally, science writer
Purdue Agricultural Communications
(765) 494-9809

Purdue News Service: (765) 494-2096;

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