Section 2. Testing Protocols and Quality Assurance Controls
In November 2004, USDA announced that its rapid screening test, Bio-Rad Enzyme Linked Immunosorbent Assay (ELISA), produced an inconclusive BSE test result as part of its enhanced BSE surveillance program. The ELISA rapid screening test performed at a BSE contract laboratory produced three high positive reactive results.40 As required,41 the contract laboratory forwarded the inconclusive sample to the APHIS National Veterinary Services Laboratories (NVSL) for confirmatory testing. NVSL repeated the ELISA testing and again produced three high positive reactive results.42 In accordance with its established protocol, NVSL ran its confirmatory test, an immunohistochemistry (IHC) test, which was interpreted as negative for BSE. In addition, NVSL performed a histological43 examination of the tissue and did not detect lesions44 consistent with BSE.
Faced with conflicting results, NVSL scientists recommended additional testing to resolve the discrepancy but APHIS headquarters officials concluded no further testing was necessary because testing protocols were followed. In our discussions with APHIS officials, they justified their decision not to do additional testing because the IHC is internationally recognized as the "gold standard." Also, they believed that conducting additional tests would undermine confidence in USDA's established testing protocols.
http://www.usda.gov/oig/webdocs/50601-10-KC.pdf
NOW, what did Dr. Detwiler try to tell them back a few years ago, around about the time before she ........ retired
USDA 2003
We have to be careful that we don't get so set in the way we do things that
we forget to look for different emerging variations of disease. We've gotten
away from collecting the whole brain in our systems. We're using the brain
stem and we're looking in only one area. In Norway, they were doing a
project and looking at cases of Scrapie, and they found this where they did
not find lesions or PRP in the area of the obex. They found it in the
cerebellum and the cerebrum. It's a good lesson for us. Ames had to go
back and change the procedure for looking at Scrapie samples. In the USDA,
we had routinely looked at all the sections of the brain, and then we got
away from it. They've recently gone back.
Dr. Keller: Tissues are routinely tested, based on which tissue provides an
'official' test result as recognized by APHIS
.
Dr. Detwiler: That's on the slaughter. But on the clinical cases, aren't
they still asking for the brain? But even on the slaughter, they're looking
only at the brainstem. We may be missing certain things if we confine
ourselves to one area.
snip.............
Dr. Detwiler: It seems a good idea, but I'm not aware of it.
Another important thing to get across to the public is that the negatives
do not guarantee absence of infectivity. The animal could be early in the
disease and the incubation period. Even sample collection is so important.
If you're not collecting the right area of the brain in sheep, or if
collecting lymphoreticular tissue, and you don't get a good biopsy, you
could miss the area with the PRP in it and come up with a negative test.
There's a new, unusual form of Scrapie that's been detected in Norway. We
have to be careful that we don't get so set in the way we do things that we
forget to look for different emerging variations of disease. We've gotten
away from collecting the whole brain in our systems. We're using the brain
stem and we're looking in only one area. In Norway, they were doing a
project and looking at cases of Scrapie, and they found this where they did
not find lesions or PRP in the area of the obex. They found it in the
cerebellum and the cerebrum. It's a good lesson for us. Ames had to go
back and change the procedure for looking at Scrapie samples. In the USDA,
we had routinely looked at all the sections of the brain, and then we got
away from it. They've recently gone back.
Dr. Keller: Tissues are routinely tested, based on which tissue provides an
'official' test result as recognized by APHIS
.
Dr. Detwiler: That's on the slaughter. But on the clinical cases, aren't
they still asking for the brain? But even on the slaughter, they're looking
only at the brainstem. We may be missing certain things if we confine
ourselves to one area.
snip...
FULL TEXT;
Completely Edited Version
PRION ROUNDTABLE
Accomplished this day, Wednesday, December 11, 2003, Denver, Colorado
2005
National Veterinary Services Laboratory (NVSL) Immunohistochemistry (IHC) Testing Summary
The BSE enhanced surveillance program involves the use of a rapid screening test, followed by confirmatory testing for any samples that come back "inconclusive." The weekly summary below captures all rapid tests conducted as part of the enhanced surveillance effort. It should be noted that since the enhanced surveillance program began, USDA has also conducted approximately 9,200 routine IHC tests on samples that did not first undergo rapid testing.
http://www.aphis.usda.gov/lpa/issues/bse_testing/test_results.html
TSS