The USDA announced late Tuesday that a cow in Mabton, Wash., had tested positive for mad cow disease.

The FDA has "a couple of teams on the ground in Washington" attempting to trace where the material from the cow went, but so far it does not know if the tissue was processed into pet food, Dr. Lester Crawford, FDA's deputy commissioner, told United Press International.

"If we determine that some of it was headed for pet food, we would likely recall that," Crawford said. But he noted the agency would not take any action until it gets confirmation, which probably will occur on Monday.

The main threat among pets is cats because they "are susceptible to BSE," he said.

Crawford said there is no way of knowing how much pet food would have to be recalled. But he said the FDA does not consider the infectious agent, called a prion, can be diluted to safe levels, so even if a small batch of infected pet food was mixed with a ton of other food, "the ton would have to be destroyed."

The most infectious parts of the diseased cattle -- the brain and spinal cord -- most likely went to a rendering facility. Some rendering plants will process those components into pet and animal feed, but others can make a variety of things, including fertilizers and building materials, that would not pose a risk to pets.

FDA officials currently are trying to track down which rendering facility or facilities received the infected cow material. From there they should know whether it made it into pet and animal feed, Crawford said. The rendering plants are required to keep records on where the material went, he noted.

Because the animal was killed relatively recently, on Dec. 9, "it is likely that the material is still on hand and has not been put into commercial channels," Crawford said. "We hope that's the case."

Michael Hansen, of Consumers Union, the watchdog group in Yonkers, N.Y., said he thinks the FDA ultimately will wind up recalling units of contaminated pet and animal feed. He noted when a case of mad cow was detected in Canada last May, authorities there requested a voluntary recall of dog food they suspected contained infectious tissue from the cow.

"They will have to recall pet food and other feed products," Hansen said. In addition, "all those rendering plants (the infected cow material passed through) will be contaminated."

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