A second animal in less than a week preliminarily tested positive for mad cow disease and it will be retested, the U.S. Agriculture Department said late Tuesday. The USDA refused to disclose any information about the suspect animal’s slaughter location, age or sex, but said the cattle carcass did not enter the human food supply. USDA officials say the government’s new, rapid tests carry a greater risk of false positives. The first U.S. case of mad cow disease was diagnosed last December in a Washington state dairy cow. In response, Japan and dozens of other countries halted purchases of American beef, valued at about US$3.8 billion annually.
The government began using rapid test kits on June 1, as part of a program to test more American cattle for the brain-wasting disease, which is believed to be spread when cattle eat the infected remains of other cattle.
More than 130 people, mostly in Europe, have died from a human form of mad cow disease, which also is known as bovine spongiform encephalopathy (BSE).
Tuesday’s test result was “inconclusive” and confirmatory results are expected back from the USDA’s animal health laboratory in Ames, Iowa, within the next 4 to 7 days, John Clifford, USDA’s chief veterinarian said. “The inconclusive result does not mean we have found another case of BSE in this country. Inconclusive results are a normal component of screening tests, which are designed to be extremely sensitive so they will detect any sample that could possibly be positive,” Clifford said in a statement.
“Screening tests are often used in both human and animal health and inconclusives are not unexpected. These tests cast a very wide net and many end up negative during further testing,” Clifford said. Last Friday, the USDA announced that another animal tested preliminarily positive for the disease also known as bovine spongiform encephalopathy (BSE). The government is still waiting for the results of a second round of more sophisticated testing to confirm if that animal was infected. As in the other pending case, the USDA’s animal health laboratory in Ames, Iowa, will retest the animal’s brain samples using more sophisticated immunohistochemistry tests, he said. The USDA said it will hold a press briefing Wednesday afternoon on the department’s mad cow testing program. Nervousness about another possible case of mad cow disease sent Chicago cattle futures contracts sharply lower Monday, but prices rose Tuesday. The June contract for live cattle futures closed up 1.7 cents at 88.8 cents per pound. An animal health expert with Colorado State University said that one inconclusive result is expected for about every 10,000 rapid tests conducted by the USDA. Barb Powers, director of the university’s Veterinary Diagnostic Laboratory System, said that as lab workers gain more experience with the rapid tests, inconclusive rates could fall to as low as one in 50,000. For example, human error in weighing tissue samples can contribute to an inconclusive result in a rapid test.
Powers’ facility is one of 12 labs USDA has approved to conduct rapid mad cow screening tests for the government.
Through Monday, the USDA said it carried out some 8,585 tests using the rapid kits.
As part of its expanded testing program for mad cow disease, the USDA plans to test about 220,000 animals from June 2004 through December 2005. That is more than a tenfold increase from the number of cattle tested last year. The National Cattlemen’s Beef Association said it was not surprised to have a second inconclusive test result emerge in less than a week.
“Until we have confirmation, we should not be alarmed,” said Terry Stokes, chief executive of the cattle group. “Inconclusive test results are not unexpected.”