Tests found that a cow suspected of harboring a second U.S. case of mad cow disease was not infected, Agriculture Department officials said Tuesday, easing concerns about the fatal disease's spread but raising new questions about the tests used to check for it.
"It's negative," a USDA spokesman told MSNBC.com.
A statement from John Clifford, deputy administrator of the USDA's Animal & Plant Health Inspection Service, said that two confirmatory tests were run on a sample from the animal in question. Both returned negative results. Two initial tests at the state level had returned positive, prompting the sample to be sent to the agency's Ames, Iowa, laboratory, the statement said.
Word of a possible second case — or "inconclusive," as industry and government officials call them — , though few details were provided about the cow's location or age.
Both factors are significant because they help trace other possibly infected animals in the U.S. herd. An animal's age shows whether it was affected by 1997 feed rules enacted by the Food and Drug Administration designed to minimize the most likely causes of the always-fatal disease, which is thought to be caused when cattle eat the infected protein of another cow.
The USDA refuses to release those details unless a cow is confirmed positive after additional testing.
"This is not an unexpected situation and proves why it is important to await the final test results," Jan Lyons, president of the National Cattlemen's Beef Association, said in a statement.
Mad cow disease, or bovine spongiform encephalopathy, eats away at an animal’s nervous system. People who eat contaminated meat can contract a related human affliction, known as variant Creutzfeldt-Jakob disease.
The most recent suspect case underscores questions about the government's testing plans.
Two earlier possible cases were reported this summer; both turned out negative. In August, USDA officials changed their testing policies, requiring multiple tests at the state level to confirm a possible case.
Since then, any possible case has been rechecked with tests on two additional samples, for a total of three. The additional samples must be found positive before the results are announced; the tissue is then sent to Iowa for confirmation using a more comprehensive test.
Bio-Rad, the California company under license to provide the testing equipment used in the state tests, said its tests "performed as expected" but did not address the rate of so-called "false positives" they expect to encounter. Initial use of the same test in Japan resulted in about one in 10,000 false positives, but those odds appear to have improved substantially.
Barbara Powers, director of the Veterinary Diagnostic Services Laboratory at Colorado State University in Fort Collins, said the odds of a false positive would be about one in 100,000 if the test is repeated according to current guidelines.
Referring to the current sample, she told MSNBC.com, "This is completely within the realm of what you'd get with a false positive."
Powers's lab is one of seven currently conducting screenings for mad cow, though the USDA has authorized thirteen facilities. Private companies and private health facilities also asked to test for the disease, but the USDA said no. Instead, the agency confirms any findings at its lab in Ames, Iowa. Powers did not say whether the sample in this case came from her facility.
The federal government for mad cow in June, saying it would check as many as 268,000 animals by the end of 2005, though officials would not set firm targets. By this week, some 121,000 samples have been checked, mostly from what the government considers the highest-risk population: older cattle, and those that fall ill or die on the farm.
All along, consumer groups and the cattle industry have tangled over federal rules designed to protect the food supply.
Fight over food and feed
Federal agencies and beef ranchers maintain that USDA rules enacted last January effectively block any possibly contaminated meat from the food supply. Those rules include a ban on high-risk tissues like cows' brains and spinal cords as well as meat from injured cows, known as downers, that cannot walk on their own.
Those rules were imposed after the first U.S. case of mad cow disease was confirmed last December. The USDA initially maintained that the lone infected cow in that case was a downer, but relented after multiple witnesses said the cow appeared healthy.
Some consumer groups also believe the ban on high-risk meat isn't effective because of the possibility of cross-contamination in slaughter facilities and certain higher-risk tissue, such as the small intestines, that can be used in human food and animal feed.
"The rule has more holes in it than a mad cow's brain," said former USDA undersecretary Carol Tucker Foreman, now director of food policy for the Consumer Federation of America.
The latest case will also renew scrutiny of Food and Drug Administration rules governing animal feed, which critics argue could still allow the infectious proteins that cause mad cow disease to make their way back into the food supply.
FDA rules announced in January and released in July banned the use of some high-risk animal protein in food and cosmetic products — things like brains and spinal cords, as well as meat from downers.
But it delayed action on broader rules proposed in January: a ban on mammalian blood and poultry litter in cattle feed; requiring feed mills to use separate equipment for cattle feed; and prohibiting meat scraps in feed.
"This case will just reinforce this notion that the FDA has been dragging its feet," said Michael Hansen, a microbiologist and researcher for Consumers Union.
The agency said in July it would consider additional rules, but acknowledged complaints from the feed industry and the cattle industry that new regulations would cost billions and were not scientifically justified.
Because the nearly 7-year-old cow found last December was born before the 1997 regulations, many cattlemen did not see the first case as a sign of problems with the feed rules.
"That animal became infected before the FDA did anything, and it doesn't provide any evidence to suggest that they need to do more to prevent it," Gary Weber, executive director of regulatory affairs for the cattlemen's association, told MSNBC.com.
A Canadian cow was found infected in May 2003, prompting U.S. officials to shut their borders to Canadian beef. Some six months later, the first U.S. case was traced to a Washington state Holstein cow originally from an Alberta ranch.
As dozens of nations closed their borders to U.S. beef, some in the cattle industry seized upon that animal's origin to underscore that mad cow was a Canadian problem.
But an expert panel convened last winter by Agriculture Secretary Ann Veneman concluded that the disease was "indigenous to North America."