WASHINGTON — The first new case of mad cow disease in the U.S. since 2006 has been discovered in a dairy cow in California, but health authorities said Tuesday the animal never was a threat to the nation’s food supply.

The infected cow, the fourth ever discovered in the U.S., was found as part of an Agriculture Department surveillance program that tests about 40,000 cows a year for the fatal brain disease.

No meat from the cow was bound for the food supply, said John Clifford, the department’s chief veterinary officer.

“There is really no cause for alarm here with regard to this animal,” Clifford said.

Mad cow disease is fatal to cows and can cause a fatal human brain disease in people who eat tainted beef. The World Health Organization has said tests show that humans cannot be infected by drinking milk from infected animals.