Two South Korean retailers have discontinued selling U.S.-imported beef after a new case of mad cow disease was discovered in the United States.

John Clifford, the chief veterinary officer for the U.S. Agriculture Department, announced the discovery Tuesday.

“The animal was a dairy cow from the state of California. Our laboratory confirmed the findings and also indicated that it was an atypical form of BSE (bovine spongiform encephalopathy) which is a rare form of the disease. It is not likely to be attributable to infected feed, which is the method in which normally BSE would be spread from from cow to cow.”

South Korean agricultural officials say they will step up inspections of U.S. beef imports in light of Tuesday's announcement, but says it will not suspend customs clearance of U.S. beef, which would have effectively halted the imports.

Seoul imposed an import ban on U.S. beef after the initial discovery of mad cow disease. It ended the ban in 2008 after reaching an agreement with Washington, an agreement which sparked several weeks of mass street protests. South Korea imported 107,000 tons of beef in 2011.

The discovery could have an impact on current negotiations between the U.S. and Japan over a trans-Pacific trade deal. Tokyo also banned U.S. beef imports in 2003, but agreed in 2005 to limit the imports to cattle 20 months old or younger.

Japanese Chief Cabinet Secretary Osamu Fujimara told reporters Wednesday the discovery will have no bearing on the trade talks.

“Basing our information on the scientific facts, the matter in question is completely separate. The BSE (mad cow disease) situation, with regards to the discussion surrounding TPP (Trans-Pacific Partnership), has absolutely no relationship. Please clearly understand this point.''

Fujimara also said the government will not change its inspection process, since the infected cow was older than 30 months.

Clifford said at no time was human health at risk. He said the affected cow was never meant to be slaughtered for meat and that milk does not transmit the disease.

Clifford said longstanding safeguards by the United States and other countries to protect humans from mad cow disease are working. He noted there were just 29 cases of the disease worldwide in 2011 — dramatically down from the peak of more than 37,000 cases in 1992.

Mad cow disease attacks the brains of affected cattle. It is always fatal. Doctors believe people can come down with a human form of the disease by eating tainted meat.

Clifford said agriculture officials are sharing the laboratory results with the World Organization for Animal Health.