Timeline: BSE confirmed in Texas-born cow ... ... tests on index herd negative

Cattleman, The, Aug 2005

The U.S. Department of Agriculture confirmed June 29 that genetic testing had verified bovine spongiform encephalopathy (mad cow disease) in a 12-year-old cow that was born and raised in a Texas beef cattle herd.

Subsequent epidemiological investigations resulted in the culling and testing of 67 adult animals from the index herd. Bio-Rad tests for BSE were conducted on all 67 animals by the National Veterinary Services Laboratory (NVSL) in Ames, Iowa. All tests were negative.

On July 12, Texas officials lifted the quarantine on the source herd. At press time, USDA's Animal and Plant Health Inspection Service was tracing animals of the same age that had left the ranch.

Timeline

The BSE-positive animal was a Brahman-cross cow born and raised in a single Texas herd. The location of the ranch was not disclosed.

On Nov. 11, 2004, the 12-year-old cow was taken to a Texas auction market. Because of its condition, the cow was sent to Champion Pet Foods in Waco, Texas. The company produces several blends of dog food, primarily for the greyhound industry.

On Nov. 15, the animal arrived dead at Champion. Under procedures established by USDA's intensive surveillance program, a sample was sent to the USDA-approved Texas Veterinary Medical Diagnostic Testing Laboratory (TVMDL) at Texas A&M University.

Between June 1, 2004, and June 1, 2005, TVMDL tested nearly 34,000 samples from Texas, New Mexico, Arkansas and Louisiana. They tested the sample from Champion on Nov. 19 using a Bio-Rad ELISA rapid test for BSE. Initial results were inconclusive.

Because of the inconclusive results, a representative from USDA took the entire carcass to TVMDL where it was incinerated. USDA's Animal and Plant Health Inspection Service (APHIS) began tracing the animal and herd.

The sample was then sent to the National Veterinary Services Laboratory for further testing. Two Immunohistochemistry (IHC) tests were conducted and both were negative for BSE. At that point APHIS stopped their trace.

USDA scientists also ran an additional, experimental IHC "rapid" tissue fixation test for academic purposes. This test has not been approved internationally.

Some abnormalities were noted in the experimental test, but because the two approved tests came back negative, the results were not reported beyond the laboratory.

Monitoring by OIG

USDA's Office of Inspector General (OIG) has been monitoring implementation of the BSE expanded surveillance program and evaluating the following:

* Effectiveness of the surveillance program;

* Performance of BSE laboratories in complying with policies and procedures for conducting tests and reporting results;

* Enforcement of the ban on specified risk materials in meat products;

* Controls to prevent central nervous system tissue in advanced meat recovery products;

* Ante mortem condemnation procedures; and

* Procedures for obtaining brain tissue samples from condemned cattle.

While reviewing voluminous records, OIG auditors noticed conflicting test results on one sample-rapid inconclusive, IHC negative, experimental reactive.

Sample retested

At the recommendation of the Inspector General, the sample was retested during the week of June 5 with a second confirmatory test, the Western Blot. The results were reactive.

USDA scientists then conducted an additional IHC confirmatory test, using different antibodies from the November 2004 test. On Friday, June 10, Secretary of Agriculture Mike Johanns publicly announced the results as a "weak positive."

On June 16 an official with USDA's National Veterinary Services Laboratory hand-carried samples for further testing to the Veterinary Laboratory Agency (VLA) in Weybridge, England. Since 1991, the VLA has been a BSE reference laboratory for the World Organization for Animal Health (OIE).

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. They also examined the November experimental IHC test and interpreted the results to be positive.

Weybridge also conducted additional tests, including IHC, OIE-prescribed Western Blot, NaTTA Western Blot and Prionics Western Blot tests.

To better understand the conflicting results, USDA also conducted Bio-Rad and IDEXX rapid screening tests, IHC and OIE-prescribed Western Blot. USDA also used DNA sequencing to determine the prion protein gene sequence of the animal.

New testing protocol

On June 24, Weybridge confirmed that the animal was BSE positive but that the level of infection was low. Secretary Johanns called a press conference to announce the findings and a change in U.S. testing procedures.

"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.

"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."