WASHINGTON — The first new case of mad cow disease in the U.S. since 2006 has been discovered in a dairy cow in California, but health authorities said the animal never posed a threat to the nation’s food supply.
The infected cow, the fourth ever discovered in the U.S., was found as part of an Agriculture Department surveillance program that tests about 40,000 cows a year for the fatal brain disease.
No meat from the cow was bound for the food supply, said John Clifford, the department’s chief veterinary officer.
“There is really no cause for alarm here with regard to this animal,” Clifford told reporters at a hastily convened news conference.
Mad cow disease, or bovine spongiform encephalopathy (BSE), is fatal to cows and can cause a fatal human brain disease in people who eat tainted beef. The World Health Organization has said that tests show that humans cannot be infected by drinking milk from BSE-infected animals.
In the wake of a massive outbreak in Britain that peaked in 1993, the U.S. intensified precautions to keep BSE out of U.S. cattle and the food supply. In other countries, the infection’s spread was blamed on farmers adding recycled meat and bone meal from infected cows into cattle feed, so a key U.S. step has been to ban feed containing such material.
Clifford said the California cow is what scientists call an atypical case of BSE, meaning that it didn’t get the disease from eating infected cattle feed, which is important.
That means it’s “just a random mutation that can happen every once in a great while in an animal,” said Bruce Akey, director of the New York State Veterinary Diagnostic Laboratory at Cornell University. “Random mutations go on in nature all the time.”
The atypical form of BSE that is caused by protein mutation also occurs in humans. Called classic Creutzfeldt-Jakob disease, it is found at a rate of one case per 1 million people worldwide, according to the Centers for Disease Control and Prevention.
“It’s not unreasonable to think that something similar could occur in cattle,” said Terry Lehenbauer, director of the School of Veterinary Medicine Research Centers at the University of California, Davis. “We just don’t know all the science about how this disease develops and is transmitted.”
Questions remain about whether the incident will prompt the USDA to change how it tests for the disease. But Mike Doyle, director of the University of Georgia’s Center for Food Safety, said the testing system worked because it caught what is a really rare event.
“It’s good news because they caught it,” Doyle said.
Clifford did not say when the disease was discovered or exactly where the cow was raised. He said the cow was at a rendering plant in central California when the case was discovered through regular USDA sample testing.
Rendering plants process animal parts for products not going into the human food chain, such as animal food, soap, chemicals or other household products.
Dennis Luckey, executive vice president of Baker Commodities, told The Associated Press that the disease was discovered at its Hanford, California, transfer station when the company selected the cow for random sampling.
Luckey said the cow died at a dairy and was randomly tagged for the surveillance program.