USDA announces ‘non-definitive’ BSE test
—Sample bound for England for confirmatory testing.
— Sample first collected in April.
USDA announced July 27 a non-definitive test result for a brain tissue sample tested at an Animal and Plant Health Inspection Service (APHIS) lab.
The sample, which was tested at least three months after being collected, was sent to USDA by an independent veterinarian who had been called to a remote undisclosed farm in April 2005, to care for an animal experiencing calving difficulty.
Little was known about the specifics of the case as of press time last Thursday, including the origin or type of animal involved. USDA officials confirmed that they have traced the animal back to its herd of origin, and they have also confirmed that the animal was more than 12 years old, born prior to the feed ban which took effect in 1997. The herd of origin has not been quarantined, and USDA officials indicated any decision about a quarantine or further herd testing would hinge on the test results.
During a technical briefing conducted by USDA Chief Veterinarian Dr. John Clifford, indications were the animal was born in the U.S. USDA officials also confirmed that the animal was destroyed after it died on the farm while giving birth. No part of the cow made it into either human or animal food chains.
“It is important to note that this animal poses no threat to our food supply,” said Clifford.
The veterinarian removed samples of brain tissue from the animal and treated them with a formalin preservative, consistent with proper protocols at the time. The delay between sampling and testing occurred when the veterinarian forgot to forward the samples to the USDA. Sources for USDA said, while “not optimal,” the delay posed no threat to the food chain, and hailed the success of the enhanced surveillance procedures put in place in to prevent such an animal from being processed for consumption by human or animal. To date, more than 419,000 tests have been conducted with an “extremely low” incidence of BSE said officials.
Results from the test, conducted by a USDA lab, were non-definitive, suggesting the need for further testing. Samples can yield different results based solely on the tissue being tested. In this case, Clifford said, staining on the brain tissue samples indicated the presence of prion proteins, indicative of BSE, but the staining pattern was not typical and warranted confirmatory testing.
Shortly after the USDA made their statement last Wednesday, a spokesman for the department confirmed that officials were in the process of booking flights to transport a tissue sample to both the APHIS Lab in Ames, IA, and the international reference lab in Weybridge, England, for further testing. Results were expected within four to seven days of the sample reaching the labs.
Because the tissue samples had been treated with a preservative in preparation for an immunohistochemistry (IHC) test, scientists in both Ames and Weybridge will be limited solely to the IHC test instead of a combination protocol utilizing both IHC and the Western Blot test. Scientists say the Western Blot test cannot be performed on samples adulterated by preservative. — John Robinson, WLJ Associate Editor
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