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USDA Credibility?......Zilch

Mike

Well-known member
USDA explains BSE test discrepancies

Ames’s “experimental” IHC positive in November but not announced

Agency still tracing origin of mad cow case

By Pete Cilento
Foodmarket News
[email protected]


Serious questions regarding the Agriculture Department’s mad cow testing procedures have emerged after Friday’s announcement of the second case of bovine spongiform encephalopathy in the United States. The incongruity between the original immunohistochemistry tests and the subsequent Western blot, as well as the revelation of a positive rapid IHC test in November -- which was concealed by the USDA’s Ames, Iowa, lab technicians for seven months -- led several to question the effectiveness of the USDA’s testing protocol for BSE.

Further adding fuel to the fire was Agriculture Secretary Mike Johann’s disclosure that the Weybridge, England, laboratory where the sample was sent for confirmatory testing itself performed an IHC test which was positive, as opposed to the two negative IHC tests announced by the USDA in November. The Weybridge lab also confirmed the sample positive for BSE via the more comprehensive Western blot test.

Agriculture Secretary Mike Johanns and veterinary doctors from the U.S. and the U.K. attempted to explain the discrepancies in a press conference Friday. Johanns offered several possible explanations for the clash between the two iterations of IHC testing across the Atlantic.

Johanns stressed that the IHC test used by the USDA was formulated before the first case of mad cow disease in 2003, and utilizes a different set of antibodies than the Weybridge IHC test.

Variation in test conditions could also yield different results in two IHC tests, said Johanns. Factors such as temperature, chemicals used, and length of antibody exposure could all produce discrepancies in the two test results. Though Johanns said the USDA froze the sample and that in the future it would study the effects before doing so, he said the freezing in this case did not affect results.

Johanns also addressed the fact that no announcement was made after an experimental IHC test on the sample tested positive in November.

“Because the test was not validated and because it followed the two approved IHC tests that came out negative, the results were not reported out of the lab,” explained Johanns. “Again, appropriate protocols relating to additional testing for research will prevent a similar situation in the future.”

As for the incongruity between the USDA’s two IHC tests and the Western blot performed in June both in the U.S. and in England, the agency said that the abnormal prion deposits in the animal’s brain may not have been uniformly distributed. An uneven distribution could result in differing IHC results, because unlike the Western blot, which would detect prion deposits anywhere in the brain, the IHC targets a specific sector of the brain.

Though the two IHC tests the USDA ran in November were negative, the IHC performed in June in the Weybridge lab was positive. Additionally, the USDA ran another IHC test on the sample on June 13, 2005, which was also positive. All standard Western blot tests performed by both nations returned positive results.

When pressed by the media on the state of origin for the cow, the USDA would not confirm any specific locations. It would only say that there was “no evidence” the cow was an import, but said it was still conducting DNA tests to determine the state and herd of origin. Several media reports since November have indicated the cow was from the state of Texas, but the USDA did not offer confirmation.
 

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