Symptoms of mad cow disease in humans can take more than five years to incubate, and the real risk of the millions of pounds of recalled ground beef consumed over the last two years will be difficult to assess, a Johns Hopkins microbiologist said.
“The risk is very low, but it?s the fact that it?s such a terrible disease and that it?s 100 percent fatal that really scares people,” said Dr. Richard Johnson, professor of neurology and microbiology with Johns Hopkins Medicine.
USDA officials are investigating whether any “downer” cattle – cows too sick to stand up – made it into the Westland slaughterhouse in Chico, Calif., even as investigators track down 143 million pounds of beef declared unfit.
The recall came after the Humane Society of the United States released an undercover video earlier this year depicting workers kicking cows and ramming them with forklifts to force them to walk.
USDA recalled Westland slaughterhouse beef dating to February 2006, making it the largest in U.S. history. The previous record was 35 million pounds of beef by Thorn Apple Valley, recalled in 1999.
Federal officials said 37 million pounds of the latest recall was used to make hamburgers, chili and tacos for school lunches. More than 140 cases of tainted beef ended up in schools in the Baltimore region.
If a cow died of with bovine spongiform encepalopathy, the disease that causes mad cow, and wasn?t tested before slaughter, there would be no way of knowing until the disease manifests itself in humans, he said.
Mad cow has been confirmed in only three tests in the American beef industry, with one of those cows coming across the border from a Canadian ranch.
In the United Kingdom, practically the entire population was exposed to cattle that may have had mad cow since the disease was identified in the 1980s, Johnson said. Fewer than 200 humans died from eating the meat.
The method of infection is little understood, but scientists suspect a protein called a prion can cause the disease, even if the meat?s fully cooked, Johnson said.
Symptoms in humans include prominent psychiatric or behavioral symptoms, a painfully distorted sense of touch, and delayed neurologic response.
About 40,000 food animals are inspected for mad cow each year in the United States, USDA spokesman Jim Rogers said. “The parts of the animal most likely to pass on the prion protein – the brains and the spinal chord – are removed anyway,” he said.
