The department has also been trying to track the whereabouts of 81 cows originally thought to have been imported with the infected cow from Canada September 4, 2001, via a port in Oroville, Washington.

One of those cows has been tracked to a dairy farm in Mattawa, Washington, USDA Chief Veterinarian Ron DeHaven told reporters. As a result, he said, authorities this week placed that cow's herd under quarantine.

That brings to 11 the number of the 82 cows that have been accounted for, he said. The others are the cow in which BSE, or mad cow disease, was diagnosed and the nine animals the infected cow was with when it was taken to the slaughterhouse, he said.

A 12th cow is believed to be in Canada, DeHaven said.

"The whereabouts of the remaining 70 animals has still yet to be confirmed," he said, adding that officials have "good leads on those."

Officials are also trying to track the whereabouts of the infected animal's bull calf and its mother, DeHaven said.

The animals are under quarantine not because there is concern that they could have contracted BSE from the infected cow, but because it is possible they shared the same food source, he said.

Cattle feed containing parts from infected cows are blamed for the spread of the disease. Officials say the infected animal was born about 6.5 years ago, before Canada and the United States banned such feed.

Next week, laboratories in Canada and the United States are expected to have results of DNA tests officials hope will confirm whether the infected cow indeed came from Canada.

U.S. officials have said an ear tag taken from the cow at slaughter shows the animal came from Edmonton, the same province where Canadian officials found their first case of the disease in a cow last May.

But Canadian officials have said that ear tags are not definitive proof, and have sought the DNA tests.

DeHaven said it was "too premature" to determine whether the two cases could be traced to the same food source.

Officials were still trying to determine how to implement an order announced this week by Agriculture Secretary Ann Veneman banning "downer" cows, which cannot stand, from entering the food supply.

BSE can make it impossible for infected cows to stand. The disease is of concern to public health officials because it can cause variant Creutzfeld-Jakob disease, a fatal brain disorder, in humans.

DeHaven said arrangements are being made to test the cows at rendering plants that process meat that is not for human consumption.

Inspectors will condemn any animal determined to be non-ambulatory "and ensure that it's humanely handled until it is, in fact, euthanized by the establishment, then denatured," said Dr. Daniel Engeljohn, of the FDA's Food Safety and Inspection Service.

So far, no animals have been sacrificed, but "it is safe to presume that some or all of those animals will need to be sacrificed," DeHaven said.

The decision about quarantining is not wholly based on science, DeHaven said, acknowledging the tremendous impact that public perception has had on the industry. Beef prices have tumbled and a number of countries have banned U.S. beef imports since the discovery of the lone U.S. case.

Only the infected animal's birth cohort or immediate relatives represent any risk, but "public perception concerns" might dictate that even animals from the same herd may be sacrificed, he said.

Already, the case has had an impact on the job front.

A spokesman for Fremont Beef in Fremont, Nebraska, said Friday that the company laid off 49 of its 131 workers in the last week due to bans of U.S. beef imports. Eighty percent of Fremont's sales came from exports to Japan, which is one of several countries that have banned U.S. beef.

Curry Roberts, president of PM Beef Holdings, a meat processor in Richmond, Virginia, said his company has not laid off anyone, but may have to do so as early as next week.

Spokespersons for Excel Beef and Swift & Company, the nation's No. 2 and No. 3 beef processors respectively, said it was too soon to tell if overseas beef bans would lead them to cut their workforce.