The first U.S. case of mad cow disease in six years sparked fears of illness that prompted at least one major South Korean retailer to suspend the sale of American beef.
However, public health officials said the risk of Americans contracting the disease is low, given that the affected dairy cow in central California never entered the human food chain and did not contract bovine spongiform encephalopathy through contaminated animal feed.
"It was never presented for slaughter for human consumption, so at no time presented a risk to the food supply or human health," said John Clifford, the Agriculture Department's chief veterinarian.
Sarah Klein, food safety attorney for the Center for Science in the Public Interest, said there is no need for consumers to take precautions.
"A case of a single cow with bovine spongiform encephalopathy is not a reason for significant concern on the part of consumers, and there is no reason to believe the beef or milk supply is unsafe," she said.
"If the cow were exposed to the typical strain of BSE via animal feed -- and the government says that's not the case here -- that would have represented a significant failure," she said.
She said the government would have had a difficult time tracking down other cattle that may have been eating the same feed because the nation lacks an effective animal identification program.
In South Korea, one of the world's largest importers of U.S. beef, the discovery of BSE, also known as mad cow disease, was enough to prompt retailer LotteMart to remove American beef from store shelves.
"Currently, the sale of U.S. beef is temporarily suspended to ease our customers from anxiety," LotteMart said.
The South Korean government said it will step up checks on U.S. beef imports, but not halt them for now.
In 2010, South Korea imported 125,000 tons of U.S. beef, a 97% increase from the year before, the U.S. Department of Agriculture said.
The cow's carcass was at a Baker Commodities Inc. rendering facility in Hanford, California, according to company Executive Vice President Dennis Luckey.
The company renders animal byproducts and had randomly selected the animal for testing on April 18, he said.
"We are in the business of removing dead animals from dairies in the Central Valley," he said. "As part of that program, we participate in the BSE surveillance program."
The sample was sent to the University of California at Davis for initial testing, which came back inconclusive. It was then sent to the Department of Agriculture's laboratory in Ames, Iowa, where it tested positive, the agency said.
The carcass was in quarantine Wednesday.
"We're waiting now for USDA to tell us how to dispose of it," Luckey said.
He would not say where the cow was from, but Rep. Devin Nunes, R-California, said it was from a dairy farm in Tulare County. "We did trace it back to a farm," Nunes said, adding that the discovery "demonstrates the strength of our surveillance system."
In a statement, California Department of Food and Agriculture Secretary Karen Ross said CDFA veterinarians were working with the USDA to determine whether other cows are at risk. "Feed restrictions in place in California and around the country for the last 15 years minimize that risk to the greatest degree possible," she said.
Eating contaminated meat or some other animal products from cattle that have BSE is thought to be the cause of Creutzfeldt-Jakob disease.The fatal brain disease was blamed for the deaths of 150 people in Britain, where there was an outbreak in the 1980s and 1990s.
In people, symptoms of the disease include psychiatric and behavioral changes, movement deficits, memory disturbances and cognitive impairments.
BSE can cause infected animals to display nervousness or aggression, difficulty in coordination and standing up, decreased milk production or weight loss.
It is usually transmitted between cows through the practice of recycling bovine carcasses for meat and bone meal protein, which is fed to other cattle.
In this case, the Agricultural Department reported that the cow had a rare form of BSE not likely carried by contaminated feed.
Agriculture Secretary Tom Vilsack said Monday that he remains confident in the health of the national herd and the safety of beef and dairy products.
"This is an atypical case, which means it's not connected in any way, shape or form to feed. ... A very rare circumstance and situation," Vilsack said. "It can just sort of come up and pop up -- sometimes it's genetic."
Since 2004, the USDA has removed the brain and the spinal column -- the parts suspected of causing mad cow disease in humans -- from the food system.
Unlike most other meat-borne illnesses, such as those caused by E.-coli bacteria, cooking does not kill
the infectious agent that causes mad cow disease.
Consumers who wish to exercise extra caution can follow the advice presented by the Web-based consumer advocacy group Consumeraffairs.com, which advises the avoidance of brains, neck bones and beef cheeks, bone marrow and cuts of beef that are sold on the bone. The group also says to choose boneless cuts of meat and ground beef only if it has been ground in the store.
"Evidence shows that our systems and safeguards to prevent BSE are working, as are similar actions taken by countries around the world," said the USDA's Clifford.
Last year, 29 cases of BSE were reported worldwide, down 99% from the peak of 37,311 cases in 1992.
"This is directly attributable to the impact and effectiveness of feed bans as a primary control measure for the disease," he said.
The Agriculture Department confirmed the first case of mad cow disease in America on December 23, 2003, in a cow born in Alberta, Canada, in April 1997, only four months before the United States and Canada began banning the use of brain and spinal cord tissue in cattle feed.
A second U.S. case was confirmed June 24, 2005, and a third on March 13, 2006.
The infected California cow confirmed Tuesday was America's fourth case of mad cow disease.