Mad cow disease kills cows and some of the people who eat the meat of infected cows. The disease has spread widely in Europe, and many people fear that it could spread to the United States, although so far it hasn't. The disease is caused by a rogue protein, called a prion. Prions are smaller than viruses and are not killed by the heat and chemicals that kill bacteria and viruses, making them particularly difficult organisms to fight.
The disease fills the cow's brain with holes, making it look like a sponge. An infected cow will show changes in temperament that may include nervousness, aggression, abnormal posture, poor coordination, trouble getting up, decreased milk production, and weight loss. There is no treatment for the disease, and all cows that get it will die. The incubation period is between two and eight years, and it takes two weeks to six months for cows to die after symptoms appear.
Although only cows can contract mad cow disease, humans can be infected with the human form, called Creutzfeld-Jakob, from eating tainted beef.
Countries that have had recent cases of mad cow disease include the Czech Republic, Ireland, Northern Ireland, France, Germany, Greece, Portugal, Slovakia, Slovenia, Spain, Switzerland, Netherlands, Belgium, Denmark, Luxembourg, Liechtenstein, Italy, and Japan.
There is no lab test to detect the mad cow disease in live animals. It is confirmed only during autopsy by microscopic examination of brain tissue and molecular detection of the prion that causes the diseases.
The U.S. Department of Agriculture conducts strict surveillance of livestock to ensure against the transmission of mad cow disease to the United States.
Sheep, humans, cows, elk, deer, mink, rats, mice, hamsters, and possibly monkeys get a variation of the disease.
In 1982, researcher Dr. Stanley Pruisner, a biochemist at the University of California at San Francisco, identified prions as being responsible for causing mad cow and the human version of the disease, Creutzfeld-Jakob disease. Although his work is still controversial, it is now fairly widely accepted that prions exist and cause these diseases. In 1997, Dr. Pruisner received a Nobel Prize for his work.
England saw its first cases of mad cow disease in 1986. Since then, more than 170,000 cows have been diagnosed with the deadly disease. The British government has spent $7.5 billion to kill and dispose of 4.7 million cows that were old enough to develop the illness.
More than 80 people died in Britain from eating mad cow-tainted meat. Most were infected even as the government assured the public that the disease couldn't infect them. At the time the initial cases occurred, cow by-products were fed to other cows, contributing to the spread of the disease. This practice was stopped in 1989.