Confirmatory Tests Show Suspect Cow Has BSE

New protocol will include testing with IHC and Western blot test on any inconclusive tests. Compiled by staff

Published on: Jun 24, 2005

USDA received confirmatory tests from Weybridge, England, finding that a sample from an earlier inconclusive cow does have bovine spongiform encephalopathy.

"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," says Agriculture Secretary Mike Johanns. "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. Americans have every reason to continue to be confident in the safety of our beef."

Effective immediately, if another BSE rapid screening test results in inconclusive findings, USDA will run both an IHC and Western blot confirmatory test. If results from either confirmatory test are positive, the sample will be considered positive for BSE.

"I want to make sure we continue to give consumers every reason to be confident in the health of our cattle herd," Johanns adds. "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."

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 World Animal Health Organization, or OIE, as a world reference laboratory for BSE. 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.