Host: As news of California's first confirmed case of mad cow disease in Kings County, south of Fresno ripples across the globe, federal officials insist the beef supply is safe. But consumer advocates have their doubts, as the California Report's Central Valley Bureau Chief Sasha Khokha explains.

Sasha Khokha: The cow that tested positive died on a dairy farm. Before it was sent to a rendering plant, it was randomly selected to be tested for mad cow disease. Meat from infected cows can cause a related, and fatal, illness in humans. But federal officials say consumers shouldn't panic: the cow in question was never going to become hamburger, and mad cow disease can't pass through milk.

John Clifford: Our livestock is some of the healthiest in the world, and consumers should be confident in our food supply.

Khokha: That's USDA Chief Veterinary Officer John Clifford. He says this case proves the government's testing system works. But the watchdog group that publishes Consumer Reports isn't so sure. Michael Hansen, a senior scientist with Consumers Union, says the government tests fewer than 50,000 animals a year for mad cow disease. About 34 million cattle were slaughtered in the U.S. last year.

Michael Hansen: We have no idea how widespread this is. Without further testing, we just don't know. But the fact that they found something should give us pause for concern.

Khokha: Hansen says if consumers are worried, they should avoid pre-packaged ground beef, hot dogs, or sausages, which may include meat from many cows.