WASHINGTON (AP) – The United States has what may be its first homegrown case of mad cow disease, confirmed a full seven months after officials first suspected the animal might be infected.

Despite the delay in reliable results, the government says the food safeguards 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,” Agriculture Secretary Mike Johanns said during a news conference Friday.

Still, the emergence of a native-born case could cast a shadow over the nation’s 96 million cattle, the largest herd in the world. Taiwan announced Saturday it was immediately renewing its ban on the importation of U.S. beef.

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 2003 case involving an imported animal prompted some 50 nations to ban U.S. beef imports.

Japan, once the largest importer of U.S. beef, and some other countries have yet to lift those bans. Taiwan, which just two months ago lifted its ban, moved quickly to block further imports.

“The Cabinet office made this decision today,” said Chen Lu-hung, an official in the food control section of the island’s Heath Department.

In the year before the ban, Taiwan imported more than $76 million in American beef and beef products, according to the Agriculture Department.

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.

“Frankly, we have said all along that we expected additional positive test results,” Johanns said. “One positive result out of 388,000 tests in our enhanced surveillance program indicates that the presence of the disease is extremely, extremely low.”

An internationally recognized laboratory in Weybridge, England, confirmed the new case Friday after U.S. tests produced conflicting results.

The animal was a “downer” that could not walk 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 ban on downer cows is one of many safeguards aimed at keeping the disease from getting into the food or feed supply.

“There’s a better chance you’ll get hurt crossing the street to get to the grocery store than by the beef you buy in the grocery store,” Johanns said. “There is absolutely no question in my mind that Americans can and should continue to be very confident in our beef supply.”

Also banned are tissues from older cows believed to carry the disease, including the brain, skull and spinal cord. Those materials must be removed from slaughtered cows older than 30 months, because it’s believed that infection levels increase with age.

In addition, the U.S. and Canada banned the use of cattle parts in cattle feed in 1997 following the mad cow disease outbreak in Britain. Officials haven’t revealed the infected U.S. cow’s age but said it was born before the feed ban. The only known way the disease spreads is through feeding infected cattle remains to other cattle.

However, the feed ban has loopholes allowing cattle to be fed poultry litter, blood and restaurant leftovers, all potential pathways for mad cow disease. The Food and Drug Administration promised to close those loopholes last year but has not done so.

Johanns said the news should not affect efforts to lift bans on U.S. beef in Japan and Korea imposed after the first U.S. case. Japan agreed to reopen its market last fall but has not done so.

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, using the Western blot, 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.

Results from those tests came back positive, leading officials to seek confirmation from the Weybridge lab. The department also performed more tests at its lab in Ames, Iowa.

Now the department will use both IHC and Western blot when rapid tests indicate the presence of the disease, Johanns said. Consumer groups and cattlemen have criticized the department for not using the test to resolve the conflicting results.

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.

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On the Net:

Agriculture Department: http://www.usda.gov

AP-ES-06-25-05 0503EDT