The U.S. Agriculture Department confirmed on Tuesday that it found a case of bovine spongiform encephalopathy, or mad cow disease, in a dairy cow in central California though no parts of the animal entered the nation's food supply.
The USDA has begun to notify authorities at the World Organization for Animal Health (OIE) as well as U.S. trading partners, but the finding should not affect the nation's beef exports, said John Clifford, the USDA's chief veterinary officer.
U.S. cattle markets plunged on rumors of the case earlier in the trading day.
The case marks the fourth time mad cow, which is believed to cause a deadly brain disease in humans who eat infected parts from animals with the disease, has been discovered in the United States.
The carcass of the cow, which the USDA said was infected by an "atypical" form of the disease, has been destroyed. The cow was not believed to have contracted the disease by eating contaminated food, the USDA added.
"There is really no concern for alarm here with regards to this animal. Both human health and animal health are protected with regards to this issue," Clifford told reporters at a briefing at USDA headquarters.
The cow, which was from California, was found at a rendering plant, the USDA said, adding it was still tracing the exact life of the infected animal.
Rendering plants process diseased or sick animals into non-edible products that are used in such things as soap, glue, solvents, shoe polish, and anti-freeze.
Ahead of the announcement, rumors of the case pushed live cattle futures on the Chicago Mercantile Exchange down by as much as the 3-cent-per-lb daily limit. The first outbreak of mad cow in the United States occurred in late 2003, roiling global trade in beef.
"The impact should not affect exports. Now, I'm not saying it may or may not, but it should not," Clifford said, noting that the United States has been recognized by authorities as having taken steps to control its risks for the disease.
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