The government is investigating a possible new case of mad cow disease (search), but says there is no threat to the U.S. food supply.
Testing indicated the presence of the disease in a cow that died on the farm where it lived, John Clifford, the Agriculture Department's (search) chief veterinarian, said Wednesday. The animal was burned and buried, the department said.
"It is important to note that this animal poses no threat to our food supply because it did not enter the human food or animal feed chains," Clifford said.
The cow probably was born in the United States and was at least 12 years old, Clifford said. He said the cow had complications while giving birth.
The department knows the location of the farm but is not disclosing it, he said. There currently is no quarantine on the farm.
The department is conducting further tests at its laboratory in Ames, Iowa, and is sending tissue to be tested by the internationally recognized laboratory in Weybridge (search), England. Results should come in the next week, he said.
Two other cases of mad cow disease have been confirmed in the U.S. One was confirmed last month, in a Texas cow that died in November. The other was in a Canadian-born cow discovered in December 2003 in Washington state.
In this case, testing options are limited. The brain sample was preserved with formalin, making it unsuitable for all but one type of testing: immunohistochemistry, or IHC.
That test returned conflicting results on the Texas cow.
"It is possible for an IHC test to yield differing results depending on the slice of tissue that is tested," Clifford said. "Therefore, scientists at our laboratory and at Weybridge will run the IHC test on additional slices of tissue from this animal to determine whether or not it was infected."
Two additional tests, rapid screening and Western blot, were used in the Texas and Washington state cases.
The animal died in April, but the veterinarian who removed the brain forgot to send in the sample until last week, Clifford said.
"While that time lag is not optimal, it has no implications in terms of the risk to human health," he said. "The carcass of this animal was destroyed. Therefore, there is absolutely no risk to human or animal health from this animal."
Since the suspect cow's death, the department has changed its rules and no longer allows tissue to be preserved in formalin. Samples now must be shipped immediately, while they are fresh.
While testing in Ames has indicated the presence of mad cow disease, the sample did not look like a typical case of BSE, Clifford said. He said it did not have the normal distribution of prions, the misfolded mad cow protein that kills brain cells and leaves spongy holes behind.
Clifford said the possibility of another case should not hinder efforts to persuade Japan to lift a ban on U.S. beef imposed after the Washington state case. Japan, which purchased $1.5 billion in beef in 2003, agreed to lift its ban last fall but still has not done so.
He noted the animal in question was born before 1997, when the U.S. banned the practice of adding ground-up cattle remains to cattle feed. The only way cows are known to get the disease is by eating brain and nerve tissue of already-infected cows.
The brain-wasting disease is known medically as bovine spongiform encephalopathy (search), or BSE. In people, eating meat products contaminated with BSE is linked to about 150 deaths from a fatal disorder called variant Creutzfeldt-Jakob (search) disease. Most of the deaths were in the United Kingdom, where there was an outbreak in the 1980s and 1990s.
Of the 96 million U.S. cattle, the government has tested more than 419,000 for mad cow disease.