A second American animal has tested positive for mad cow disease, Agriculture Department officials said Friday night. The sample, from a downer cow in Texas that died in November, was retested earlier last week at the request of the USDA inspector general's office.
The animal had been deemed disease-free last fall, but when a sample was subjected to a more precise test, the result was a "weak positive," said USDA Secretary Mike Johanns. He said that because of the differing results from the two tests, the sample would be sent this week to the world's top mad cow lab in Weybridge, England, for a final set of testing.
Johanns said repeatedly Friday night that the new result did not mean that people face any greater health risk from eating beef, because meat from the animal did not enter the human food chain, or the beef feed chain. He also said the result should not have an impact on long and difficult negotiations underway to resume the exporting U.S. beef to Japan and Korea, or the reopening of the Canadian border to live cattle.
But if the positive finding is confirmed in England, the international reaction against U.S. beef that occurred when a Washington state dairy cow tested positive in December 2003 could be repeated.
Although the first U.S. mad cow case involved an animal born and raised largely in Canada and then shipped to Washington state, USDA chief veterinarian John Clifford said Friday night that the agency had "no information" that the possible second case was "an imported animal." He said the Texas animal was a beef cattle and was older.
He did not indicate, for instance, whether the animal was born before or after the United States implemented a ban on feeding animal parts to cows in 1997. Mad cow infection is only known to spread through the consumption of beef parts that were fed to some cows in the 1990s, and the 1997 feed ban was designed to keep mad cow disease from spreading through the U.S. herd.
The three Canadian animals that have tested positive for mad cow disease, as well as the Washington state animal, were all found to have been born before the feed ban. If an animal born after the feed ban tests positive, the effectiveness of the ban could be called into question.
Over the past year, the USDA has tested about 375,000 animals as part of an enhanced surveillance program and has found only three inconclusive results, Johanns said. Those three were each further tested using the internationally recognized immunohistochemistry, or IHC, method, and all came out negative.
But the inspector general, an independent arm of the USDA, asked for an additional test because of some discrepancies in the initial findings. The office also asked USDA to use the Western blot method of testing, which many scientists believe is more precise. Johanns said the positive result was confirmed Friday.
Mad cow disease, or bovine spongiform encephalopathy (BSE), has in rare cases been transmitted to people who eat the infected meat. The brain-wasting infection in humans, known as variant Creutzfeldt-Jakob disease, is always fatal and has killed about 150 people, most of them in Britain.
Johanns said it was unusual for a sample to test BSE-negative in one test and positive in another, but that it has happened in Europe.
Although Johanns said the new finding should not affect efforts to normalize the international beef trade, others may disagree. Japan, which used to buy more U.S. beef than any other nation, closed its market to American beef after the first mad cow case and has resisted strong pressure to reopen it. Japan, where more than 15 cows have tested positive for mad cow disease, now tests every cow slaughtered. Its government has asked U.S. producers to do the same, but the U.S. government has said the universal testing was not necessary.
The USDA has also been trying to lift a U.S. ban on live Canadian cattle that was imposed after Canada's first BSE case in May 2003. The border was scheduled to reopen in March, but a federal judge in Billings, Mont., ordered a temporary halt at the urging of beef ranchers and producers who argued the Canadian BSE-prevention system was inadequate.