U.S. Agriculture Secretary Ann Veneman says investigators are tracing the path of a slaughtered cow with mad cow disease to see if any by-products reached the American public.
In an interview Wednesday, on the Cable News Network, Ms. Veneman also said her agency is preparing an initial recall of about 4,500 kilograms of beef that may have been tainted.
News of the diseased cow in the Pacific coastal state of Washington triggered a rush by Asian governments to slap import bans on U.S. beef.
Japan, South Korea, Singapore, Malaysia, Taiwan, Australia and Thailand stopped U.S. imports Wednesday. Russia also announced a ban.
Japan is the world's leading importer of U.S. beef, and other East Asian countries are close behind.
Secretary Veneman says U.S. officials remain confident that the nation's food supply is safe and that the current risk to human health is minimal.
Ms. Veneman says meat from the Holstein cow in question - which was slaughtered December 9 - traveled through three processing plants before test results indicated a problem. Further test data is expected soon.
Humans who eat meat from infected cows can acquire a brain disease that leads to paralysis and death. The disease has killed more than 100 people worldwide since it was discovered in Britain in 1986.
Tuesday's announcement by the U.S. Agriculture Department led to an immediate drop in stock prices of the international fast-food chain McDonald's.
Mad cow disease (bovine spongiform encephalopathy) is spread when cows eat ground-up cattle feed that includes products from cows already infected with the illness.