Harkin, D-Iowa, who has been critical of the two agencies in the past, will look into whether the safeguards they put into place were adequate to prevent the disease from infecting U.S. herds, the Senator's spokesman Matt Hartwig told UPI.

The USDA announced late Tuesday a cow in Mabton, Wash., had tested positive for mad cow disease. The concern is mad cow, or bovine spongiform encephalopathy, can infect humans and cause an always fatal, brain-wasting illness known as variant Creutzfeldt-Jakob disease.

"The Senator will take this very seriously and will look into how this cow contracted the disease and what the repercussions are from this," Hartwig said.

A source close to the issue, who requested anonymity, stopped short of saying Harkin would launch a Senate investigation, but noted, "This is definitely something we're going to be looking into further," including the policies of USDA and FDA regarding prevention and detection of mad cow.

The USDA and the FDA insisted in a news briefing Wednesday the safeguard measures they had put in place prior to the detection of the mad-cow-infected animal in Washington state would ensure the disease would not spread and the U.S. beef supply was safe.

USDA officials said it was uncertain how the animal had become infected or where it had originated, but the agency thinks the most probable source of infection is contaminated feed. As a consequence, it already has launched an investigation to trace down the origins of the animal and any of its herdmates that also might have become infected.

In addition, the agency recalled 10,000 pounds of beef from Verns Moses Lake Meats in Moses Lake, Wash., that was slaughtered on the same day as the infected cow and also might be contaminated.

The meat was "recalled out of an abundance of caution," USDA Secretary Ann Veneman said during the briefing.

"Our investigation is ongoing but we believe our BSE response plan that we started in 1990 ... has provided us a strong science basis on which to control this situation," Veneman said. "We continue to believe the risk to human health from this situation is extremely low."

Harkin said he will allow the USDA to finish its investigation before taking a closer look at the issue.

"We want to allow the USDA plan to proceed ... but certainly this does raise concern," Hartwig said. "We're taking it one step at a time ... and want to get all the information together in hopes of preventing another case from developing," he said.

The safeguard measures put in place by the USDA and FDA include testing so-called downer cattle, which are unable to stand -- one possible sign of mad cow disease. In addition, since 1997, the FDA has banned the feeding of tissue from cows infected with mad cow to other cattle -- a practice that is thought to have contributed to the widespread outbreak of mad cow disease in the United Kingdom in the 1980s.

However, Harkin has criticized those measures for several years as being inadequate. The Washington cow seems to offer validation of the criticisms because it was born two years after the food ban was put into place and yet still contracted the disease.

"That's absolutely frightening," because it means there could be additional infected cows, Dr. Peter Lurie, deputy director of the Public Citizen's Health Research Group, a watchdog organization in Washington, D.C., told UPI.

"Assuming this cow was infected by contaminated feed, it is unlikely this is the only animal that ate the contaminated feed," Lurie said. "If the feed ban wasn't enforced for this animal, it probably wasn't enforced for others."

Asked if Harkin plans to look into the adequacy of the feed ban, Hartwig said: "Absolutely, we're not going to rule in or rule out anything at this point." He added: "Certainly we'll want to take a look at just how this animal contracted the disease so we can make sure USDA and FDA safeguards are as strong as they can be."

A General Accounting Office report issued in 2002 found, however, that several firms had violated the feed ban and concluded the rule was inadequate to prevent the spread of mad cow through U.S. herds.

During the briefing, Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, said the agency has boosted compliance to the feed ban since 2001 -- it is now at 99 percent. He noted, however, that at least two firms are not in compliance.

A Harkin aide, who requested anonymity, told UPI: "I would say when it comes to (mad cow disease), any case of noncompliance is a reason for significant concern."

Harkin requested the GAO conduct an additional review of the compliance to the feed ban in when the case of mad cow was detected in a Canadian herd in May. That investigation is still ongoing.

Harkin also has questions about the adequacy of USDA's system for testing cows for mad cow disease. The USDA claims to have tested approximately 20,000 animals in each of the past two years, but it has refused for the past six months to provide any documentation of its claim to UPI.

Some critics have insisted testing 20,000 cattle out of the 96 million in the U.S. herd is not nearly enough to detect all the cases of mad cow that could be present.

"It is one of the things Sen. Harkin has previously asked the USDA and FDA about ... whether the existing sample size was adequate and whether it needed to be increased," the senator's aide said.

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Steve Mitchell is UPI's Medical Correspondent. E-mail sciencemail@upi.com