The discovery of mad cow disease in a dairy cow in California is being described as a combination of the U.S.'s targeted surveillance of its beef supply and random chance.
The Department of Agriculture confirmed Tuesday that the disease had been discovered in a dead cow.
In a press briefing, John Clifford, the USDA's chief veterinary officer, said the cow's meat did not enter the food supply and the carcass will be destroyed.
The animal was found at a rendering facility run by Baker Commodities in Hanford, Calif. The disease was discovered when the company selected the cow for random sampling, Baker Commodities executive vice president Dennis Luckey told The Associated Press. The cow had not shown any other signs of the disease, such as unsteadiness or low milk production.
The Department of Agriculture performs tests for mad cow disease on about 40,000 cows each year. Ronnie Silcox, a professor of animal science and a beef cattle specialist at the University of Georgia, said cows that are at high-risk of the disease, such as those that can't walk or show signs of neurological disease, are the ones routinely tested. He called the discovery of mad cow disease "incredibly, incredibly rare." "This is one out of a million, or something like that," he said. "It's probably inevitable that we find it eventually because we're actively looking for it."
The Agriculture Department confirmed Tuesday that the cow is the fourth discovered in the United States to test positive for the disease, but stressed that consumers were not at risk because the animal was not bound for the food supply.
"There is really no concern for alarm here with regards to this animal," Clifford said. "Both human health and animal health are protected with regards to this issue."
Nevertheless, two retailers in South Korea pulled U.S. beef from their stores Wednesday in response to the report of mad cow disease.
"We stopped sales from today," Chung Won-hun, a spokesman for Lotte Mart, one of the retailers, told the Associated Press. "Not that there were any quality issues in the meat but because consumers were worried."
Home Plus, the other retailer, resumed sales and cited a government announcement of increased inspection.
U.S. government officials were quick to reassure the public that the finding posed no threat to humans.
"The beef and dairy in the American food supply is safe and USDA remains confident in the health of U.S. cattle," Agriculture Secretary Tom Vilsack said in a statement. "The systems and safeguards in place to protect animal and human health worked as planned to identify this case quickly, and will ensure that it presents no risk to the food supply or to human health. USDA has no reason to believe that any other U.S. animals are currently affected, but we will remain vigilant and committed to the safeguards in place."
The Food and Drug Administration pledged to "work with the USDA to fully investigate the feed supply as part of the epidemiological investigation." And the USDA said in a statement that milk does not transmit mad cow disease.
Silcox noted that the cows processed for consumption in the U.S. are usually too young to have developed mad cow disease.