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In the Vegetarian & Vegan News...
   Prionics Response | VegSource Interactive, Inc.

Dr. Markus Moser Responds to Gary Weber
of the National Cattlemen's Beef Association

We recently ran an article entitled "USDA Mad Cow Strategy: Don't Look, Don't Find" examining the U.S. mad cow testing procedures, which appear quite inadequate compared to much of the rest of the world.

Gary Weber, a spokesman for the National Cattlemen's Beef Association, took issue with our article, and wrote a response, linked here. In his response, Mr. Weber criticized Dr. Moser's test (Prionics), stating

Pit our IHC [Immunohistochemistry] test against the prionics..side by side and the only difference will be lots of false positives..extra tests with Prionics...

So while acknowleding Prionics was faster, meaning many many more cattle could be tested in the U.S. versus using the current IHC method, Weber objected to it because, he said, it could show the presence of BSE in a cow when confirmatory testing would show this to be a wrong result (a "false positive").

Here is the unedited response to Mr. Weber from Dr. Moser of Prionics:

April 8, 2001

BSE Surveillance is a very complex issue and the points raised in Mr Nelson's article "USDA Strategy: Don't Look, Don't Find," as well as the letter by Mr. Weber of the National Cattlemen's Beef Association deserve some detailed comments on the questions regarding the quality of both BSE-tests and BSE-surveillance.

Mr. Weber claims that unlike the classical method used for BSE-analysis by the USDA (the so-called immunohistochemistry or IHC), the Prionics-Check would produce false positive results.

He must have confused the Prionics-Check test with other rapid tests, which indeed bear the problem of false positive results. I agree that it does not make sense to use unreliable tests in a country which so far has not detected any BSE: This would only add confusion rather than clarity. But Prionics-Check has been used now for over two years in Switzerland for continuous BSE-surveillance, and during all this time there has not been a single incidence of a false positive analysis.

Prionics-Check has been developed focusing on its performance under field conditions. It uses a technology that is not prone to false positive results. In the BSE-test evaluation conducted by the European Commission (EC) in 1999 it has been the only test that reached 100% sensitivity and specificity without having to repeat tests. In other words: Prionics-Check was the only test that diagnosed all samples correctly in one go.


 



The EC evaluation contained a small second part in which dilutions of liquefied tissues were analyzed. The author of the VegSource article erroneously concluded from the results of this study that the Bio-Rad test must be more sensitive than the Prionics-Check.

In fact, the EC never made such a claim and furthermore clarified in an FAQ sheet published on the internet (http://europa.eu.int/comm/food/fs/bse/bse21_en.html) that dilution experiments represent an artificial system falling short in certain ways to represent the natural situation.

The reason for this is twofold: The first reason has to do with the fact that BSE-tests detect prion protein aggregates. The aggregates as formed in visibly ill cattle do not adequately mimic the rare aggregates formed during earlier stages of the disease. Therefore, dilutions of aggregates from visibly ill cattle do not in many ways represent the situation in BSE-infected animals at earlier disease stages. The second reason why the dilution study does not reflect field performance lies with the technical specifications of Prionics-Check: the innovative process of Prionics-Check already starts at the tissue preparation using special proprietary solutions. The dilution-tests were performed with standard liquefaction and not according to the Prionics-Check procedure used in the field.

An adequate method of determining a test's performance is the parallel testing in the field with a gold standard (e.g. immunohistochemistry) and the BSE-test which has to be evaluated. Such an evaluation, however, is extremely time- and cost intensive, but it tells you exactly how the test performs under field conditions and with naturally infected BSE animals.

Such an evaluation was done with Prionics-Check under the supervision of the Swiss Veterinary Office (it took roughly a year to get the whole Swiss evaluation done as compared to an afternoon to test the few dilutions of the EC). The extensive comparative field evaluation demonstrated that the Prionics-Check test is at least as sensitive as optimally performed immunohistochemistry in spotting naturally infected BSE animals under field conditions. Such a study has not been done for the Bio-Rad test, however, even in an experimental system performed under optimal conditions on experimentally infected animals, this test was not more sensitive than immunohistochemistry.

Reliability was a key-feature of Prionics-Check to convince European countries to follow the Swiss BSE-surveillance model and to introduce Prionics-Check for mass screening. The screening was pioneered by France and Denmark, the other countries followed.

BSE-cases started to shoot up as a result of the increased surveillance (the interested reader finds a short document on the milestones leading to the general acceptance of BSE-surveillance by mass screening at http://www.prionics.ch/PDF/surveillance_milestones.pdf). Over 2.5 million Prionics-Check tests have been sold so far throughout Europe of which over one million tests have already been carried out. Germany and Italy, two countries which previously had been allegedly BSE-free, had to face the first BSE-cases shortly after the introduction of mass screening using Prionics-Check.

Should we be afraid of introducing Prionics-Check mass testing in countries without a previous record of BSE? After all, the general picture Prionics-Check created in Europe is that whoever introduces the test will have to face a harsh reality!

So why introduce the test?

Well, not every country that introduces testing will necessarily find BSE: some may instead produce excellent evidence that they are in fact BSE-free. Let's have a look at Europe again: Both Italy and Germany were classified by the European Commission as countries with a relatively high BSE-risk, even before Prionics-Check detected the first BSE cases. This classification was based on an analysis of the two countries import and feeding practises. It was therefore not a big surprise for scientists when the first BSE-cases were found.

In contrast, both the U.S.A and Austria are classified as having a low BSE-risk (The interested reader finds the detailed risk analysis for the U.S.A. at http://europa.eu.int/comm/food/fs/sc/ssc/out137_en.pdf). Austria has introduced Prionics-Check in January 2001 and has tested so far over 30,000 animals without a single BSE-case showing up. (In Germany a cow exported from Austria recently tested falsely positive with a competitive rapid test, which caused quite a crisis for a few days until it was clear that the result was false positive. This episode of course confirmed Austria in their decision to exclusively use Prionics-Check).

Although in a Europe with open internal borders it cannot be excluded that isolated rare BSE-cases might also show up in Austria, the results of the mass screening program already demonstrates that the country is essentially BSE-free compared to its neighboring countries.

Prionics-Check therefore does not only bring the bad news of BSE, it may as well serve to demonstrate a country's BSE-free status. The risk of detecting BSE versus the advantage of demonstrating the absence of BSE - you can't have one without the other!

Dr. Markus Moser
Prionics AG
University of Zurich
Switzerland
http://www.prionics.ch


Editor's Note :

It is interesting to note that in Dr. Moser's response above, he reveals Austria has tested about 30,000 cows since January, 2001. Prionics further reports that Austria is testing all slaughtered cattle over 30 months of age, which amounts to roughly 15,000 animals a month, plus fallen stock and emergency slaughtered cattle, which adds 500 to 1,000 cows tested per month. This brings the Austrian total to about 16,000 tests per month.

During the same period that Austria is testing more than 15,000 cows per month, the U.S. has been testing fewer than 200 cows per month.

If a small country with a comparatively minute meat industry can test at this scale in order to assure their food is safe, why isn't the U.S. doing the same -- or much more?

Jeffrey Nelson
vegsource.com

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