The U.S. Department of Agriculture says new laboratory tests have confirmed the nation's first case of Mad Cow Disease. The announcement came Thursday after more than 20 countries suspended imports of U.S. beef, citing health reasons.

The U.S. Department of Agriculture said tests by British experts have confirmed an earlier analysis, by American scientists, on a cow traced to a dairy farm in the northwestern state of Washington.

The department said the British laboratory will conduct final tests to confirm its own findings that the cow had Bovine Spongiform Encephalopathy（牛海綿狀腦病）, a brain-wasting illness commonly known as mad cow disease.

But the department said it fully expects final results will be consistent with those of the tests already performed.

Cows usually become ill after eating animal feed that contains parts from BSE-infected cattle, especially the spine and brain. Humans can contract a deadly variant of BSE, known as Creutzfeldt-Jakob disease, by eating contaminated meat.

Creutzfeldt-Jakob has killed more than 100 people worldwide since it was discovered in Britain in 1986.

U.S. officials say they are trying to find the source of the infection and to determine whether any more cows have been infected with BSE.

U.S. Agriculture Secretary Ann Veneman, who announced initial test results on Tuesday, says the nation's food supply is safe and the risk to human health is minimal. More than 20 countries, including Japan, Mexico and South Korea, the three largest importers of U.S. beef, have so far suspended all imports.

Some scientists point out that cattle feed containing animal parts has been officially banned in the United States since 1997. They say the fact that a cow could become infected in spite of the ban shows glaring weaknesses in the government's attempts to protect the food supply.

In any event, U.S. agricultural officials are taking no chances and have ordered the recall of 4,700 kilograms of meat that passed through the same slaughterhouse as the infected cow.

Unfortunately for U.S. meat exporters, foreign governments have also decided they ought to take no chance with the health of their citizens.