The first suspected case of mad cow disease (search) in the U.S. was detected in Washington state on Tuesday, but officials assured Americans that their food is safe to consume.

A single Holstein (search) cow tested positive for the disease, but it had already been slaughtered and distributed.

Agriculture Secretary Ann Veneman (search) said the slaughtered cow was screened earlier this month and any diseased parts were removed before they could enter the food supply and infect humans. Fear of the disease has brought economic ruin on beef industries in Europe and Canada.

"We remain confident in the safety of our food supply," Veneman told a hastily convened news conference.

 Japan and South Korea halted imports of U.S. beef on Wednesday, depriving American exporters of two of their largest overseas markets. Singapore, Thailand, Malaysia, Taiwan and Australia followed suit.

The farm near Yakima (search), Wash., where the cow originated, has been quarantined as officials trace how the animal contracted the disease and where its meat went.

"Even though the risk to human health is minimal, we will take all appropriate actions out of an abundance of caution," she said.

Mad cow disease, known also as bovine spongiform encephalopathy, eats holes in the brains of cattle. It sprang up in Britain in 1986 and spread through countries in Europe and Asia, prompting massive destruction of herds and decimating the European beef industry.

A form of mad cow disease can be contracted by humans if they eat infected beef or nerve tissue, and possibly through blood transfusions. The human form of mad cow disease so far has killed 143 people in Britain and 10 elsewhere, none in the United States. Blood donors possibly at risk for the disease are banned from giving.

Wary of the potential economic impact on their American market, beef producers quickly sought Tuesday to reassure consumers that infected meat wouldn't reach their tables. "There is no risk to consumers based upon the product that came from this animal," said Terry Stokes, chief executive of the National Cattlemen's Beef Association.

Veneman also assured Americans the screening system worked, and no foul play was suspected. "This incident is not terrorist-related," she said. "I cannot stress this point strongly enough."

President Bush was briefed a few times on the development Tuesday and was confident Veneman's department handling the matter properly, the White House said.

With an election year approaching, the news concerned some in Congress. Rep. Tim Holden, D-Pa., a member of the House Agriculture Committee, said he expected lawmakers to hold hearings when they return to Washington in late January.

"We're going to look into this and see the possibility of how this happened," Holden said. "I'm sure there will be extensive oversight hearings to see what we can do to assure the American people the safety of the food chain."

Lawmakers are keenly aware that a case of mad cow disease in Canada last May — which officials described as a single, isolated incident — still had devastating economic consequences.

"If it's anything like what happened in Canada, it will be bad. The problem won't be that people will stop eating meat in the United States; the problem is the exports will be shut down like we did with Canada," said Rep. Collin Peterson, D-Minn.

Veneman said the Holstein, which could not move on its own, was found at a farm in Mabton, Wash., about 40 miles southeast of Yakima, and tested preliminarily positive for the brain-wasting illness on Dec. 9. Parts of the cow that would be infected — the brain, the spinal cord and the lower part of the small intestine — were removed before the animal went to a meat processing plant.

Samples from the cow have been sent to Britain for confirmation of the preliminary mad cow finding, Veneman said. The results will be known in three to five days. Veneman said consumers can get daily updates by reading the department's Web site or by calling 1-866-4USDACO.

Alisa Harrison, a department spokeswoman, said downer cattle that show signs of mad cow disease when they reach the slaughterhouse are tested for the illness.

But Rep. Gary Ackerman, D-N.Y., said such cows shouldn't be in the food supply in the first place. The Senate passed such a ban earlier this year, but it failed to make it through the House.

"I blame it on greed, greed, greed," Ackerman said. "The greed of the industry, the greed of the lobbyists and the greed of the members of Congress."

Veneman said the Agriculture Department has had safeguards in place since 1990 to check for mad cow disease and 20,526 cows had been tested in 2003 in the United States. An estimated 130,000 downed cattle are slaughtered each year.

"This is a clear indication that our surveillance and detection program is working," Veneman said.

U.S. beef remains "absolutely safe to eat," she said.

"We see no reason for people to alter their eating habits," she said. "I plan to serve beef for my Christmas dinner."

The Associated Press contributed to this report.