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From: TSS ()
Subject: The IHC Test Variables (USA BSE SURVEILLANCE)
Date: June 24, 2005 at 7:59 pm PST

The IHC Test Variables:

• IHC has been the primary confirmatory test for

USDA’s BSE surveillance program and is recognized

by the World Organization for Animal Health, or OIE.

• IHC allows scientists to determine if a sample is

positive for BSE in two distinct ways:

1.) A staining technique (presence of abnormal

prion protein) that uses antibodies to detect

abnormal prion protein in the brain.

2.) A visual examination to determine whether there

are lesions (holes or "spongy" appearances)

present in the brain.

• Several variables could yield conflicting results:

o IHC is not a standardized, commercially

available test. It involves variables, including

several options in types of antibodies and other

reactive agents. The sensitivity of any given test

is influenced by those variables.

o If the level of infectivity in the animal is extremely

low, the abnormal prion in the brain will be

minimal and therefore more difficult to detect.

o Variations in the conditions under which the

staining process is performed, such as

chemicals and reactive agents used,

temperature and length of antibody exposure,

can also cause the test to yield different results.

Testing History on This Animal:

• In November 2004, a sample from this animal

returned inconclusive for BSE on a Biorad screening

test.

• The sample was subjected to an IHC confirmatory

test, which returned negative.

• USDA scientists also ran an additional, experimental

IHC "rapid" tissue fixation test for academic purposes,

which can be conducted more quickly than the IHC

confirmatory test and is therefore of interest to the

scientific community, but it has not been approved

internationally.

• While some abnormalities were noted in the

experimental IHC test results, because the test was

not a validated procedure, and because the two

approved IHC tests came back negative, the results

were not considered to be of regulatory significance

and therefore were not reported beyond the

laboratory.

• A Western blot test conducted the week of

June 5, 2005, returned positive for BSE.

• An additional IHC confirmatory test conducted the

week of June 13, 2005, by USDA scientists utilizing

different antibodies from the November 2004 test,

confirmed this case as weakly positive for BSE.

• The Veterinary Laboratories Agency in Weybridge,

England, conducted a series of diagnostic tests

including an IHC, using different antibodies from

those used by USDA in November 2004, which

returned positive results for BSE.

• Experts from the Weybridge lab confirmed the

accuracy of the results of USDA’s November

confirmatory IHC test, concurring that the case could

not have been confirmed on the basis of this sample.

• Weybridge experts also examined the November

experimental IHC test and interpreted the results to

be positive.

Potential Causes of Conflicting Results:

• USDA scientists are consulting with Weybridge

scientists to determine the cause of the conflicting

IHC test results.

• Several factors could cause or contribute to the

discrepancy as follows:

o This animal had a very low level of infectivity and

therefore the sensitivity of USDA’s routine IHC

test might not have been sufficient to detect the

disease.

o Weybridge experts indicate that deposits of

abnormal prion in the brain tissue were not

uniformly distributed and were present at low

concentration, which means that even adjacent

samples of brain tissue might not give identical

results.

Factsheet

Veterinary Services June 2005

APHIS

USDA Protocol Review:

• USDA will develop a protocol to conduct dual

confirmatory tests, the IHC and the Western blot,

when the screening test, the Biorad, returns an

inconclusive result.

• USDA and Weybridge scientists are in agreement

that the Biorad test is a very effective and appropriate

screening test.

• USDA scientists will consult with Weybridge scientists

to assess the array of antibodies available for use in

IHC confirmatory tests to determine the most

appropriate for use in United States confirmatory

tests. Those consultations will be repeated periodically.

The U.S. Department of Agriculture (USDA) prohibits discrimination

in all its programs and activities on the basis of race, color,

national origin, sex, religion, age, disability, political beliefs, sexual

orientation, or marital or family status. (Not all prohibited bases

apply to all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille,

large print, audiotape, etc.) should contact USDA’s TARGET

Center at (202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office

of Civil Rights, Room 326–W, Whitten Building, 1400

Independence Avenue, SW, Washington, DC 20250–9410 or call

(202) 720–5964 (voice and TDD). USDA is an equal opportunity

provider and employer.

Safeguarding American Agriculture Animal and Plant Health Inspection Service • United States Department of Agriculture •

http://www.usda.gov/documents/vs_bse_ihctestvar.pdf

THIS confirms that the June 2004 Enhanced BSE cover-up, was just that. Like i said before, due to this terribly flawed system, those 388,000 testing to date for BSE in the USA were meaningless and should be retested. ...

TSS




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