MAD COW DISEASE IN USA

WASHINGTON (Reuters) Apr 24 - U.S. authorities reported the first U.S. case of mad cow disease in six years on Tuesday and quickly assured consumers and global importers that meat from the California dairy cow did not enter the food chain.

John Clifford, the USDA's chief veterinary officer, said the case was "atypical" and that there was "no cause for alarm" from the animal. Cows can contract the disease spontaneously in rare cases but it cannot be transmitted unless the brain or spinal tissue is consumed by humans or another animal. The infected cow in this case had not entered the food chain.

Mad cow, or bovine spongiform encephalopathy (BSE), is believed to cause the deadly brain disease variant Creutzfeldt-Jakob in humans who eat infected parts from animals with the disease. The first mad cow case in the United States was in late 2003 and caused the nation's beef exports to drop by nearly $3 billion the following year.

There is no evidence that humans can catch it from drinking the milk of an infected cow. However, fears of a potential backlash among consumers and big importers of U.S. beef caused Chicago live cattle futures to drop sharply.

The USDA has begun notifying authorities at the World Organization for Animal Health (OIE) as well as U.S. trading partners, but the finding should not affect the nation's beef exports, Clifford said. The USDA is still tracing the exact life of the infected animal.

The carcass of the cow, which the USDA said was infected by an "atypical" form of the disease, is under quarantine and would be destroyed. The cow, which was found at a rendering plant that processes diseased or sick animals into non-edible products for use in things like soap or glue, was not believed to have contracted the disease by eating contaminated feed, the USDA said.

"There is really no concern for alarm here with regards to this animal. Both human health and animal health are protected with regards to this issue," Clifford told reporters at a briefing at USDA headquarters.

Dennis Luckey, executive vice president of Baker Commodities Inc, a privately held Los Angeles-based processor of animal byproducts and used cooking oil, confirmed the carcass was handled by one of his company's facilities.

The carcass of the dairy cow was brought to the collection facility in Hanford, California, last Wednesday and a tissue sample was taken from its brain and sent to the University of California, Davis. The sample came back inconclusive and was then sent to the USDA facility in Ames, Iowa, and returned on Tuesday as positive.

"The material is in quarantine now," Luckey said, adding that Baker Commodities is waiting on direction from USDA on how to dispose the carcass

BSE was first diagnosed in the United Kingdom in 1986, according to the Office of the United States Trade Representative. Reported cases peaked in peaked at 37,316 in 1992, of which 99.9% were in the United Kingdom.

The first U.S. case was reported in an animal imported from Canada in 2003, while other cases were reported in 2005 and 2006, according to the agency.

Scientists said that as the dairy cow had not been eaten by other animals, there was no risk of the disease being spread.

"There's always been concern that there could potentially be a spontaneous form of mad cow disease that just arrives and doesn't get transmitted through feed," George Gray, director of George Washington University's Center for Risk Science and Public Health.

"It's not like classic mad cow disease that's transmitted by animals being exposed to the infectious parts of other animals."