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From: TSS ()
Subject: USDA botched testing of mad cow suspect
Date: July 22, 2005 at 11:07 am PST


USDA botched testing of mad cow suspect
By Steve Mitchell
Medical Correspondent
Jul. 21, 2005 at 5:44PM

U.S. Department of Agriculture officials tracing cattle that may have been associated with the country's first case of mad cow disease in 2003 botched the testing of a cow considered "at risk" and did not run a confirmatory test called a Western blot, according to agency documents obtained by United Press International.
The documents, obtained via the Freedom of Information Act, show a pattern that is similar to how the agency handled a Texas cow that was initially ruled negative but seven months later was found to be positive for the deadly disease on the Western blot test.
The cow related to the 2003 case appears to have arrived from Canada in the same herd as the infected animal and resided at the same dairy cattle finishing farm in Washington state. The USDA found the animal at a farm in Mabton, Wash., and was testing it for mad cow -- formally known as bovine spongiform encephalopathy, or BSE -- because it was deemed to be at risk for the disease.
The USDA documents indicate an ELISA rapid test was run that turned out negative. This was followed by a test called immunohistochemistry, or IHC, that also came back negative, but the result was coded as "loc" instead of the usual "neg."
A note in the document states the "loc" notation "means that the IHC test was negative, but the wrong location of the brain was sampled for testing. There is no longer any possibility to test the proper location."
BSE experts said the notation did not make sense and questioned why the agency did not run a Western blot test, which may have helped determine if the cow was carrying BSE.
"That's bizarre," Markus Moser, a molecular biologist and chief executive officer of Prionics, a Swiss firm that manufactures BSE test kits, told UPI.
"If the ELISA has been done on the correct piece of brain, then it was done on the obex," Moser said. "If it was done correctly, then it was done on one hemisphere of the obex and you have the other hemisphere for IHC or another test. If they say they don't have any correct tissue for doing that, then what exactly did they use for the first ELISA?"
If the ELISA test was run on an incorrect portion of the brain, then its results are unreliable.
USDA officials acknowledged there were problems with the brain sample.
"The person who collected the sample made a notation that the sample was not a good sample, meaning it could have been torn or mangled," agency spokeswoman Amy Spillman told UPI.
This applied only to the IHC test, however. She said there was no indication the sample was unsuitable for the ELISA test.
"They didn't make any notes the sample wasn't viable for ELISA, so we would assume it would be acceptable for" that test, Spillman said.
Moser said he still would run the Western blot test in a case like this, even if the correct brain region was not available.
Another renowned BSE testing expert agreed it would have been appropriate to run the Western blot test.
The expert, who spoke to UPI on condition of anonymity, said there are several reasons why the obex may have been damaged or found to be unsuitable for IHC tests.
"The best you can do is to throw more tests at it," the expert said, "especially ones that concentrate prion protein (thought to be the mad cow agent), such as the SAF Immunoblot (Western blot), and if that still comes up negative too, forget it."
Spillman said the Western blot was not run because it "wasn't part of our protocol then."
The USDA also failed to run the Western blot on the Texas cow that last month was deemed positive, making it the second case of the disease detected in U.S. herds.
That cow had tested positive on two rapid tests last November, but the agency subsequently ran an IHC test and told the public it had come back negative. It was not until June -- and at the insistence of the agency's inspector general -- that the USDA would run a Western blot that came back positive.
In announcing the June results, the USDA also informed the public that one of three IHC tests run in November had come back positive. This was not disclosed in November, and the revelation still has experts questioning why the agency would ignore a positive result and not run further tests -- such as a Western blot -- to determine more precisely if the cow was infected.
The finding of a BSE-infected cow can have major economic consequences. A recent study conducted by Kansas State University researchers calculated the U.S. beef industry already has lost billions of dollars in exports due to foreign nations closing their borders in response to the 2003 mad cow case.
In the past, the USDA has been quick to use the Western blot to confirm or rule out cases. In 1997 two cows that initially were suspected of having mad cow were tested using both the IHC and Western blot. Neither showed evidence of infection. Even in the 2003 case, the infected animal was retested using Western blot to confirm it had the disease.
The USDA changed its policy after the Texas cow blunder, stating it would run both the IHC and the Western blot on cows that initially test positive on rapid tests.
Michael Hansen, with the watchdog group Consumers Union, said the agency's failure to run the Western blot raises questions about the validity of the BSE surveillance program.
"You don't know whether it's incompetence or some nefarious scheme, but its very Keystone Coppish," said Hansen, a biologist and senior research associate with CU.
"Neither of those possibilities -- gross bureaucratic incompetence or political interference suggesting a coverup -- instills confidence in the public that the agency is doing the right thing," he told UPI.
Another BSE expert told UPI of a similar problem with the USDA lab on a sheep that was tested for scrapie, a similar disease to BSE. The expert had observed the brain being extracted from the sheep and knew it was the correct region for testing, but the USDA lab later said it received the wrong brain region.
UPI previously reported that from 2001 to 2003 the USDA collected the wrong part of the brain in more than 200 cows that were being screened as part of its BSE surveillance program.
The USDA documents also indicate the agency never was able to identify or test 52 cows that came into the United States in 2001 along with the Washington cow that tested positive in 2003. Of these, 11 were considered to be "high risk" because they were born within a year and on the same premises as the infected cow.
These cows may have gone into the food supply and been consumed by people. The concern is humans can contract a fatal brain disease from eating beef products contaminated with the mad cow pathogen.
"It's possible those animals went to slaughter, but (USDA) would've done ante-mortem inspection and if those animals had exhibited signs (of BSE) they wouldn't have been allowed into the food chain," Spillman said.
Hundreds of seemingly healthy animals in Europe have tested positive for the disease, however, and several eyewitnesses said the infected Washington cow was walking and did not appear ill the day of slaughter.
The USDA's inability to locate these cows demonstrates the need for a stronger animal-identification program so officials can trace the final destinations of animals if there is a problem, Hansen said.
--
E-mail: sciencemail@upi.com

http://www.washtimes.com/upi/20050721-043953-6306r.htm

TSS




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