WASHINGTON - US authorities reported the country's first case of mad cow disease in six years, swiftly assuring consumers and global importers there was no danger of meat from the California dairy cow entering the food chain.

Agriculture Secretary Tom Vilsack gave assurances that the finding posed "no risk to the food supply or to human health", a line that seems to have been accepted by major foreign buyers.

Fears of a potential backlash among consumers and big importers of US beef fueled a sell-off in Chicago live cattle futures on Tuesday, with memories still sharp of the first case in 2003 that caused a $3 billion drop in exports. It took until 2011 before those exports fully recovered.

Mexico, South Korea, Japan and the European Union - among the markets for overseas US beef sales - will continue imports, although two major South Korean retailers halted sales of US beef.

A woman picks up a box of Australian beef as local (L) and Australian beef (R) are displayed on a stand at Lotte Mart in Seoul April 25, 2012. Two major South Korean retailers halted sales of US beef after an outbreak of mad cow disease as the country's agriculture ministry looked set to move towards banning quarantine inspections, a move that would effectively end imports. Lotte Mart, a unit of Lotte Shopping Co, said it had suspended sales due to what it said was "customer concerns", as did Home Plus, a unit of Britain's Tesco PLC. The Korean characters (front R) reads, "Please understand that we suspend sales of US beef from April 25". [Photo/Agencies]

Russia's health watchdog said it could consider restrictions on US imports but that it was waiting for more information on the outbreak and the planned US response before taking a decision.

Experts said the case was "atypical", meaning it was a rare occurrence in which a cow contracts the disease spontaneously, rather than through the feed supply.

The risk of transmission generally comes when the brain or spinal tissue of an animal with BSE, or mad cow disease, is consumed by humans or another animal, which did not occur in this case.

First discovered in Britain in 1986, the disease has killed more than 150 people and 184,000 cows globally, mainly in Britain and Europe, but strict controls have tempered its spread. The first US case was found in late 2003 in an animal imported from Canada, followed by two more in 2005 and 2006. Two of those cases were also "atypical".

"I would say this is an extremely isolated, atypical event," said Dr. Bruce Akey, professor of veterinary medicine and director of the Animal Health Diagnostic Center at Cornell University, which tests for Mad Cow and Chronic Wasting diseases for New York state and several Northeastern states.

"There is still no evidence at all that BSE is anything but an extremely rare event in the United States and nothing that poses a threat to the human or animal food chain."

Import restrictions from major customers could deal a fresh blow to companies such as Tyson Foods Inc and Brazil-based JBS.

Korean retailer Lotte Mart, a unit of Lotte Shopping Co, said it had suspended sales due to what it said was "customer concerns", as did Home Plus, a unit of Britain's Tesco PLC.  

Not in the feed

The USDA has begun notifying authorities at the World Organization for Animal Health (OIE) as well as US trading partners, said John Clifford, its chief veterinary officer.

"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," Vilsack said in a statement.  

The USDA is still tracing the exact life of the infected animal, and the carcass of the cow is under quarantine and will be destroyed.  

The cow was found at a rendering plant, which processes diseased or sick animals into mainly non-edible products for use in products such as soap or glue.

Live cattle futures on the Chicago Mercantile Exchange

edged higher in Asian trade on Wednesday after falling by the daily 3-cent-per-pound limit in the previous session. The June live cattle contract was up 0.4 percent at 112 cents per lb by 0736 GMT.