WASHINGTON, July 27 (UPI) -- U.S. Department of Agriculture officials said Wednesday they may have detected a possible third case of mad cow disease among the country's herds.
A 12 year-old cow showed positive staining on a test known as immunohistochemistry, but the results were different from what typically is seen with the disease, USDA chief veterinarian John Clifford said during a news briefing.
The USDA is retesting different sections of the animal's brain and sending it to experts at a internationally recognized lab in Weybridge, England, for additional testing.
"There was some staining present but it did not match a normal pattern and we're taking additional parts of the brainstem to see if we can find a normal staining pattern as well as sending samples to Weybridge," Clifford said.
Clifford said the carcass had been destroyed and did not enter either the human or animal food chain. He said all indications are the cow originated in the United States and was not imported.
A brain sample from the animal originally had been collected by a private veterinarian in April, but the individual forgot to send it into the USDA until last week.
The sample had been preserved in a chemical called formalin, which makes it impossible to run other tests, including rapid and Western blot tests. USDA officials announced last month that a cow they originally had determined to be free of mad cow last November actually tested positive using the Western blot test.
Clifford declined to release additional details about the cow until the USDA confirmed it was indeed infected, but he said the agency already knows where the cow originated and will announce further details if the infection is confirmed. The USDA had difficulty tracking down the cow that tested positive in June.
To date, two cases of mad cow disease have been confirmed in U.S. herds: the first in a cow in Washington state in December 2003, and in a Texas cow last month.
The concern about the disease is humans can contract an incurable and fatal brain disorder called variant Creutzfeldt Jakob disease from consuming beef products contaminated with the mad cow pathogen.
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