No meat from the animal — a dairy cow in central California — entered the food chain, he said.
Only four U.S. cows have ever been found with the disease, which was first identified in livestock in 1985.
The first case was confirmed in 2003 in Washington state and caused beef exports to plunge, leading to billions in losses for U.S. livestock producers.
Consuming tainted beef can be fatal to humans, though drinking milk from a diseased cow may not be harmful, the World Health Organization has said.
The last major outbreak of the disease in humans occurred in the United Kingdom in the early 1990s and was linked to more than 150 deaths.