DIANE SAWYER (ABC NEWS)(OC): Good evening. We begin with a headline we did not expect to see again, mad cow disease in this country. Today the Department of Agriculture confirmed a new case of mad cow in California. It has been six years since the last scare, and a lot of precautions were taken then. So how did this cow get sick? And how dangerous is this development? ABC's David Wright has the latest.
DAVID WRIGHT (ABC NEWS)(VO): Rarely does the health of a single cow have billion dollar implications, but in this case it does.
DAVID WRIGHT (ABC NEWS)(VO): Because it's America's first confirmed case of bovine spongiform encephalitis in six years. BSE is mad cow disease, a potentially deadly brain-wasting infection that can be transferred to humans.
DOCTOR JOHN CLIFFORD (US DEPARTMENT OF AGRICULTURE): The animal was a dairy cow from the state of California. Our laboratory confirmed the findings.
DAVID WRIGHT (ABC NEWS)(VO): Today the chief veterinary officer for the USDA cautioned, this is an isolated case, not the start of an epidemic.
DOCTOR JOHN CLIFFORD (US DEPARTMENT OF AGRICULTURE): Our livestock population is some of the healthiest in the world. And the consumers should be confident in our food supply.
DAVID WRIGHT (ABC NEWS)(VO): Everyone still remembers the devastating outbreak of mad cow disease in Britain during the 90s. 150 people died.
DAVID WRIGHT (ABC NEWS)(VO): After the first case of mad cow disease was confirmed in this country in 2003, dozens of countries banned US beef. Shipments dropped more than 80%. China still bans US beef imports. Today the USDA insisted this fourth confirmed case occurred at a rendering plant for products other than food.
DOCTOR JOHN CLIFFORD (US DEPARTMENT OF AGRICULTURE): This particular animal did not enter the food supply at any time. So there is no concern about that.
DAVID WRIGHT (ABC NEWS)(VO): But the USDA currently tests only 40,000 cows of years of the millions that are slaughtered.
SARAH KLEIN (FOOD SAFETY ATTORNEY FOR CSPI): USDA has not completed their investigation of this particular case. And so we'll be watching carefully to see what they find. Obviously if it turns out that we have tainted feed, we will have a much larger problem on our hands.
DAVID WRIGHT (ABC NEWS)(OC): Now it is a mystery how this cow in Hanford, California contracted the disease. Apparently it was not from tainted feed which had been the source of previous outbreaks. But the FDA and the USDA will be testing the feed supply anyway. Diane?
DIANE SAWYER (ABC NEWS)(OC): And the government advice to consumers, David?
DAVID WRIGHT (ABC NEWS)(OC): Well, they say that the beef is safe. Don't forget the burgers and the steaks off the grill at this point. However, food safety advocates have been warning that stricter safeguards should be put in place. But cattlemen have resisted them, Diane.