US 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 US
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 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 said it would maintain beef trade with the US, while Japan, which only imports US 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 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.   - Reuters