(ENS) WASHINGTON -- A second U.S. animal has tested positive for mad cow disease, Agriculture Secretary Mike Johanns said June 24. Effective immediately the U.S. Department of Agriculture is adding a second diagnostic test to its protocol for determining whether suspect cattle are infected with the fatal brain wasting disease.
The U.S. Department of Agriculture (USDA) has received final test results from The Veterinary Laboratories Agency in Weybridge, England, confirming that a sample from an animal that was blocked from the food supply in November 2004 has tested positive for bovine spongiform encephalopathy (BSE), commonly called mad cow disease.
The suspect animal was a downer cow, one unable to walk, so it never entered the food chain, Johanns said.
It was one of the three suspect animals whose brain tissue had been tested three times since November, using three different procedures. Results were positive for one cow on one of the three tests. The other tests were either inconclusive or negative for all three cows.
The tests performed at Weybridge confirmed BSE in the cow that had tested positive in one U.S. test.
Johanns directed USDA scientists to work with international experts "to thoughtfully develop a new protocol that includes performing dual confirmatory tests in the event of another "inconclusive" BSE screening test.
"We are currently testing nearly 1,000 animals per day as part of our BSE enhanced surveillance program, more than 388,000 total tests, and this is the first confirmed case resulting from our surveillance," Johanns said.
Effective immediately, if another BSE rapid screening test results in inconclusive findings, the USDA will run both an immunohistochemistry (IHC) and Western blot confirmatory test. If results from either confirmatory test are positive, the sample will be considered positive for BSE, Johanns said.
Both tests are accepted by the OIE, the World Animal Health Organization.
"This confirmed case of BSE in no way impacts the safety of our nation's food supply," said Johanns.
"I want to make sure we continue to give consumers every reason to be confident in the health of our cattle herd," the secretary said. "By adding the second confirmatory test, we boost that confidence and bring our testing in line with the evolving worldwide trend to use both IHC and Western blot together as confirmatory tests for BSE."
"I am encouraged that our interlocking safeguards are working exactly as intended. This animal was blocked from entering the food supply because of the firewalls we have in place," he said. "Americans have every reason to continue to be confident in the safety of our beef."
Only one case of mad cow disease had been confirmed previously in the United States, in a dairy cow in Washington State in December 2003. Since then, preliminary tests indicated the possibility of the disease in three cows, but further testing had ruled out any infection.
USDA has initiated an epidemiological investigation to determine the animal's herd of origin. That investigation is not yet complete. The animal was born before the United States instituted a ruminant-to-ruminant feed ban in August 1997, which prevents the use of most mammalian protein in cattle feed.
According to internationally accepted research, feed containing meat-and-bone meal is the primary way BSE is transferred to the cattle population.
The animal was selected for testing because, as a non-ambulatory animal, it was considered to be at higher risk for BSE. An initial screening test on the animal in November 2004 was inconclusive, triggering USDA to conduct the internationally accepted confirmatory IHC tests. Those test results were negative.
Earlier this month, USDA's Office of the Inspector General recommended further testing of the seven-month-old sample using another internationally recognized confirmatory test, the Western blot. Unlike the IHC, the Western blot was reactive, prompting USDA to send samples from the animal to the Weybridge laboratory for further analysis.
The laboratory in Weybridge, England, is recognized by the OIE as a world reference laboratory for mad cow disease. Weybridge officials this week conducted a combination of rapid, IHC and Western blot testing on tissue samples from the animal in question. At the same time these diagnostic tests were being run by Weybridge, USDA conducted its own additional tests.
As a non-ambulatory, or "downer" animal, the cow was prohibited from entering the human food supply, under an interim final rule in effect since January 2004. Research has shown that BSE is most likely to be found in older non-ambulatory cattle, animals showing signs of central nervous system disorders, injured or emaciated animals, and cattle that have died for unexplained reasons. USDA's testing program targets these groups of animals for testing.
The system of human health protections includes the USDA ban on specified risk materials, or SRM's, from the food supply. SRM's are most likely to contain the BSE agent if it is present in an animal.
Additional measures, such as a longstanding ban on importing cattle and beef products from high-risk countries, a ruminant-to-ruminant feed ban, U.S. slaughter practices, and aggressive surveillance provide a series of interlocking safeguards to protect U.S. consumers and animal health.
As the epidemiological investigation progresses, USDA pledged to continue to communicate findings in "a timely and transparent manner."
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