WASHINGTON -- The latest confirmed case of mad cow disease in the United States has been traced to a beef cow born in Texas 12 years ago and slaughtered last November at a pet-food plant, Agriculture Department officials said yesterday.
It was the first time the disease has been confirmed in a US-born cow. The other US case, confirmed in December 2003 in Washington state, was in a dairy cow imported from Canada.
The department's chief veterinarian, Dr. John Clifford, said the new case was identified and linked to the herd in Texas through DNA testing. He said the herd had been quarantined and that no part of the infected animal entered the food or animal feed chain.
''The animal did not enter the human food chain. The safety of our food supply is not in question," Clifford said in a conference call with reporters. He said the government would not identify the cow's owner or the town it came from. It was born and raised on the same farm, he said.
He said that given the cow's age, officials believe it probably was infected before the 1997 ban forbidding the use of cattle parts in cattle feed.
Eating the brain and other nervous tissue of an animal with the brain-wasting ailment is the only way the disease is known to spread. The Agriculture Department and the Food and Drug Administration are trying to trace the history of the herd's feed.
Officials also are trying to identify herd mates born within one year of the infected cow's birth as well as any offspring born within the past two years, Clifford said.
The Agriculture Department confirmed the case last Friday but had to wait for DNA analysis to confirm the cow's origin. Tracing the cow proved difficult because the animal's breed was mislabeled and its tissues got mixed with parts from other cows. It was killed at a pet-food plant in Waco, Texas, but the plant rejected using it.
Pets are not considered at risk from eating cattle remains, which are frequently ground up and added to their food as protein. Cattle remains are also allowed in feed for pigs and chickens.
Officials said beef from Texas and the rest of the United States is the safest in the world.
''Though we must continue to be vigilant about our food supply, the fact is that US beef is safe," said Senator John Cornyn, Republican of Texas. ''It's clear to me that our safeguards worked as designed."
Officials suspected last November that the cow was infected because initial screening had indicated the presence of the disease. But more sophisticated tests came back negative, and a new round of tests was done this month.