Testing Confirms U.S. Case of Mad Cow

Following inconclusive tests by the U.S. Department of Agriculture (USDA, Washington, DC, USA), a cow slaughtered in November 2004 in the United States has only recently been confirmed by tests in a UK laboratory to have bovine spongiform encephalopathy (BSE), known as mad cow disease.

The initial screening of the sample was conducted by USDA scientists with an enzyme-linked immunosorbent assay (ELISA). This test provided inconclusive results, according to the scientists. Immunohistochemistry tests (IHC) were also performed, which were negative. However, a Western blot test, which is more sensitive, was only recently recommended by the USDA's Office of the Inspector General and it showed a positive result. Following this, the USDA sent animal samples to a laboratory in Weybridge (UK) for confirmation. The Weybridge laboratory is recognized by the World Animal Health Organization as a world reference laboratory for BSE. The British tests have since confirmed that the animal had BSE. The USDA states that DNA tests will be conducted to locate the herd the diseased animal came from.

Critics of the USDA have complained about the long delay in getting an accurate diagnosis, and have called for changes in the testing regimen. This has already begun, according to the USDA. Effective immediately, if another BSE rapid screening test results in inconclusive findings, both an IHC and a Western blot test will be run. If results from either test are positive, the sample will be considered positive for BSE.

"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,” noted Mike Johanns, secretary of agriculture. "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.”




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