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APHIS under orders to change BSE test protocol

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Mar 2, 2005
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APHIS under orders to change BSE test protocol

Tam Moore
Oregon Staff Writer

In no uncertain terms, the secretary of agriculture directed a change in U.S. bovine spongiform encephalopathy protocols June 24. It came after he announced that an international laboratory confirmed the disease in brain tissue that USDA's National Veterinary Laboratory said was negative after two immunohistochemistry tests run in November.

"I am calling for a change in our testing. I have directed our scientists to work with international experts to develop protocol for simultaneously performing the IHC and the Western blot test in the event of another inconclusive screening test," Johanns said in his telephonic news conference. "I have also called for a careful analysis of the antibodies we are using to conduct the IHC test to make sure that we're using the most current and the best option."

It was a Western blot test – ordered by the USDA inspector general and run at a USDA Agriculture Research Laboratory – that on June 10 came up positive for BSE and set in motion the massive retesting.

This week, Ed Loyd, Johanns' spokesman, said the secretary won't get involved in writing the rule. "That's up to the scientists," Loyd said in a telephone interview.

He said the Animal and Plant Health Inspection Service, which supervises the National Veterinary Laboratory at Ames, Iowa, and the seven regional labs under contract to run initial BSE screening tests, has responsibility for getting the protocol updated and for checking it out with the international BSE Reference Laboratory in Weybridge, England.

APHIS is also scrambling to positively identify the birth herd of the BSE cow. Because carcass parts were mixed up with those of four other animals at the kill plant, APHIS is using genetics to confirm the birth herd. When that's complete, there will be an attempt to trace other animals that long ago shared the same feed supply as the victim. There had been no announcement at midweek, but Loyd said APHIS is working as quickly as it can.

John Clifford, the USDA's chief veterinarian, in the June 24 teleconference raised speculation that the animal might be what scientists call a "spontaneous" BSE case. That's estimated to be one animal in 1 million that for unexplained reasons develops the brain lesions with no apparent connection to feed contaminated with the agent thought to cause BSE.

Perhaps supporting that theory is Clifford's announcement that protein molecular patterns in composite tissue samples in those tests don't agree with patterns found in the English strain of BSE. They are closer, said Clifford, to molecular patterns for some BSE found in France. BSE was first described in 1986 in England. Before bans on live animal exports and rendered protein from cattle feed were put in place, the rare and fatal central nervous system disease spread to several European countries.

An ARS laboratory at Pullman, Wash., is tracking weights and molecular patterns of various BSE samples to determine if the agent mutates into other stains.

Among challenges for scientists rewriting the testing protocol are laboratory results that show in the U.S. BSE case, antigens generated by presence of the BSE agent called a prion were not evenly distributed throughout the tissue sample. That means one slice of tissue could indeed have no prion presence, while a sample from elsewhere in the same brain had been attacked. The Western blot tests include grinding up the sample, mixing it and increasing chance of detecting minute prion presence.

As the cattle trade continued to talk of a Texas pet food plant as the kill site, the Dallas Morning News interviewed Lelve Gayle, director of the Texas Veterinary Medical Diagnostic Lab at College Station. It runs BSE screening tests for samples collected in Texas and New Mexico.

Gayle said he didn't know if the original samples were tested at the Texas lab, and even if they were, confidentiality agreements forbid release of testing information sought by the Morning News.

The Dallas Morning News contributed to this report. Tam Moore is based in Medford, Ore. His e-mail address is [email protected].