WASHINGTON (AP) - In an effort to find the source of the most recent case of mad cow disease, the U.S. Agriculture Department says it will be using DNA tests to trace the infected animal back to its herd. The United States confirmed what may be its first homegrown case of mad cow disease Friday, seven months after officials first suspected the animal might be infected.
Pinpointing the cow's herd will help track the animal's feed and explain how it became infected. The only known way the disease spreads is through feeding infected cattle remains to other cattle, which the United States banned in 1997.
"We're pretty confident that we have the herd, but we want to make sure," John Clifford, the department's chief veterinarian. "Testing is being done now on tissue from cows that may have been herdmates."
The effort is complicated by mistakes made after the animal was killed. The cow's breed was accidentally mislabelled, and its tissues were mixed with tissues from other cows, Clifford said.
Despite the delay in reliable results, the government says the precautions are working well.
"The fact that this animal was blocked from entering the food supply tells us that our safeguards are working exactly as they should," said Agriculture Secretary Mike Johanns.
Still, the emergence of a U.S.-borne case could cast a shadow over the nation's 96 million cattle, the largest herd in the world. Taiwan, which imported more than $76 million US in American beef in 2003, announced Saturday it would immediately reimpose its import ban. Japan, once the largest importer of U.S. beef, still has not lifted its ban.
The only previous U.S. case, confirmed in December 2003, was in a dairy cow that had been imported from Canada, where three other cases have been found. Even that case involving an imported animal prompted some 50 nations to ban U.S. beef imports.
Johanns said Friday the case will have no impact on government efforts to resume the trade in live cattle from Canada.
"This does not change (our) position at all with regard to reopening the border with Canada," he said. While the animal's origin is still being investigated, he said there's no evidence it came from Canada.
The cattle trade, which was supposed to resume in March, has been stymied by a court challenge from an American ranchers' group. Two court hearings on the issue are scheduled for July.
Canada has had three cases of its own. The first, revealed in May 2003, prompted U.S. officials to shut the border to Canadian cattle. Canada's industry has been devastated, losing some $7 billion Cdn in the last two years.
Officials and some industry observers on both sides of the border have said a new U.S. case of the brain-wasting disease shouldn't hurt Canada's attempts to resume the cattle trade.
But others argue another case doesn't produce the best climate for legal arguments on dropping the import ban.
The American ranching group R-CALF United Stockgrowers of America spearheaded the legal challenge that blocked resuming the cattle trade. It argues Canadian cows are a danger to American herds.
Stan Eby, president of the Canadian Cattlemen's Association, said the discovery of the infected cow is not surprising since the mad cow disease risk is similar on both sides of the border.
While Johanns would not say where the cow turned up, he said there was no evidence it was imported.
Johanns said the new case was no surprise, given that the department is testing about 1,000 cattle a day. Since escalating its testing after the 2003 case, the government has screened about 388,000 animals.
An internationally recognized laboratory in Weybridge, England, confirmed the new case Friday after U.S. tests produced conflicting results.
The animal was a "downer" - a cow that can't walk on its own - and was delivered to a rendering plant for animals unfit for human consumption. The government banned downer cows from the food supply just days after the 2003 case.
The downer cow ban is one of many safeguards aimed at keeping the disease from getting into the food supply.
Also banned are tissues, including the brain, skull and spinal cord, from older cows believed to carry the disease. Those materials must be removed from slaughtered cows older than 30 months because it is believed that infection levels increase with age.
In addition, the United States and Canada banned the use of cattle parts in feed in 1997 following the mad cow disease outbreak in Britain.
Officials have not said how old the infected U.S. cow was but said it was born before the feed ban.
The feed ban has loopholes allowing cattle to be fed poultry litter, blood and restaurant leftovers, all potential pathways for mad cow disease.
The new case was confirmed after a series of conflicting test results.
The department did initial screening using a "rapid test," which was positive. A more detailed immunohistochemistry, or IHC test, was negative. But the department did not conduct a third round, until the department's inspector general, Phyllis Fong, ordered it to do so two weeks ago. Fong has not explained why she ordered new tests.
Mad cow disease - medically known as bovine spongiform encephalopathy, or BSE - kills brain cells and leaves spongy holes behind. A form of the disease in people is variant Creutzfeldt-Jakob disease. It has been linked to the consumption of contaminated meat. The disease has killed about 150 people worldwide, mostly in Britain.
© The Canadian Press, 2005
