Mad cow disease is a frightening and fatal brain ailment with a counterpart in humans. Some research has hinted that people can get it eating infected cattle. But agricultural and disease experts say the single occurrence in a cow in the United States is unlikely to lead to an animal or human epidemic because of government safeguards.
The term Mad Cow Disease is very descriptive. In 1986, cattle in Britain, where the disorder was first noticed, began drooling and staggering. Some were nervous, others aggressive. Autopsies showed their brains were full of holes.
"This is an abnormal protein called a prion that gets into the nervous tissue, the brain and the spinal cord." explained Veterinarian James Cullor of the University of California at Davis. "It expands and takes up space in the brain, and puts holes in the brain, makes it looks kind of like Swiss cheese."
Mad cow disease spread quickly through European dairy and cattle herds in the 1990s. It is thought to have developed in the 1970s from a centuries-old sheep disease called scrapie. Leon Thacker, a Purdue University animal disease expert, says the illness probably spread to cattle when they were given feed containing infected animal meat and bone.
"They had the practice of rendering dead cattle, putting them through a process to preserve the protein, and then feeding that material back to cattle," he said. "It's an economy of protein, which is one of the more expensive portions of animal feed. Subsequent to that, England stopped feeding cattle protein back to cattle."
In reaction, the U.S. government also ended the practice in 1997. The United States was in a better position than Europe to do this because grains and soybeans are more plentiful and cheap for animal feed.
Mr. Thacker says the feed ban has broken the pathway that could spread mad cow disease in the United States. "We're in the sixth year of a program that would essentially stop a disease that has an average incubation period of five years," he said. "So I feel fairly safe that this disease is not going to develop into a widespread national catastrophe that was seen in England just because this is the only means essentially that this disease can be spread."
At the University of California, James Cullor says the U.S. milk supply is also safe from mad cow disease. "Scientists around the world have looked at blood and milk very hard as the source of transmission, but have not found the prion to be present in those materials," he said. "So I feel that we can contain this. We [found] the sentinel animal, we can deal with it through our normal channels. This shows that our surveillance system works and it shows that our government and diagnostic lab people take this very seriously in observing for this disease."
Leon Thacker at Purdue University suggests that the single mad cow case found in Washington state earlier this month could have been a spontaneous occurrence, the result of a mutant prion in the animal's brain.
However, the U.S. Agriculture Department's announcement of the case has caused a worldwide reaction, with many countries banning imports of U.S. beef. Mr. Thacker hopes Americans do not also turn against domestic beef, but instead adopt the attitude of Canadians, who he says understood the science of the disease when they faced the same situation earlier this year.
"The consumption of beef in that country did not go down. I'm hopeful that happens in this country," he said.