Authorities reported the country’s first case of mad cow disease in six years on Tuesday, swiftly assuring consumers and global importers that there was no danger of meat from the California dairy cow entering the food chain.

Despite assurances from Agriculture Secretary Tom Vilsack that the finding posed “no risk to the food supply or to human health”, two major South Korean retailers halted sales of U.S. beef and the government there said it may suspend quarantine inspections, a move that would effectively halt imports.

Fears of a potential backlash among consumers and big importers of U.S. 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 said it would maintain beef trade with the United States, while Japan, which only imports U.S. cattle below 20 months of age after previous mad cow cases, said it would take no immediate action.

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 U.S. 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 would deal a fresh blow to companies such as Tyson Foods Inc and Brazil-based JBS that are still smarting from the “pink slime” furor.

Officials at Korea’s agriculture ministry said an outright import ban was unlikely.

“It won’t be an import ban, but possibly a quarantine suspension,” a spokesman at the Korean agriculture ministry said.

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 U.S. trading partners, said John Clifford, the USDA’s 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 would be destroyed.

The cow was found at a rendering plant, which processes diseased or sick animals into mainly non-edible products for use in things like 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 0305 GMT.