updated 6/29/2005 7:59:18 PM ET 2005-06-29T23:59:18

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 pet-food plant, Agriculture Department officials said Wednesday.

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It was the first time the disease has been confirmed in a U.S.-born cow. The other U.S. 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 none of the infected animal’s carcass 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 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 U.S. is the safest in the world.

“Though we must continue to be vigilant about our food supply, the fact is that U.S. beef is safe,” said Sen. John Cornyn, R-Texas. “It’s clear to me that our safeguards worked as designed and the animal in question never entered the human or animal feed supply.”

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 officials announced then that the suspect cow was free of the ailment.

The conflicting test results bothered the department’s internal inspector, who ordered a new round of tests earlier this month. Those results came back positive, and an internationally recognized laboratory in Weybridge, England, confirmed last Friday that the cow had mad cow disease.

Mad cow disease is medically known as bovine spongiform encephalopathy, or BSE, which causes spongy holes in the brain.

In people, a rare but fatal form of the disease called variant Creutzfeldt-Jakob disease has been linked to eating infected tissue from cows. A BSE outbreak in Britain in the 1980s and 1990s has been linked to the deaths of 150 people.

Officials said the case poses no new threat to the health of people or animals. “Downer” cows that can’t walk, such as this one, are banned from the food supply. In addition, the government requires removal of the brain, spinal column and other nerve tissues from cattle older than 30 months when they are slaughtered to keep them from entering the food supply.

Many scientists believe that mad cow proteins stay in nervous tissue such as the brain and spinal cord. Scientists also believe meat from older cows presents more of a risk because infection levels rise with age.

There are loopholes in the feed ban: Cattle are still fed poultry litter, cattle blood and restaurant leftovers, all potential pathways for the BSE protein to be fed back to cattle. The FDA promised to close the loopholes last year but still has not done so.

© 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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