Jan 28, 2004 (CIDRAP News) The US Department of Agriculture (USDA) will probably end its investigation of the nation's single bovine spongiform encephalopathy (BSE) case within 2 weeks, even if all the cows that might have shared feed with the infected cow are not found, USDA officials said this week.
Hunting for cattle that came from the infected cow's original herd in Alberta, the agency has narrowed its main search effort from 80 cows to 25 cows that were born within a year before or after the infected one, officials said. Those are the animals that could have had feed from the same source as the sick cow and thus might have been exposed to BSE (mad cow disease), the agency said. Focusing on them is in line with World Organization for Animal Health (OIE) guidelines.
Ron DeHaven, the USDA's chief veterinary officer, said at a Jan 26 briefing that 14 of those 25 cows have been found, but the other 11 may never be found. Some of them probably went to slaughter before the BSE case was discovered, and identification has probably been lost for some of the rest, he said.
DeHaven predicted the investigation will soon reach a point of "diminishing returns" as it broadens to include more and more herds that could have cows from the sick cow's original herd. "I think that we can wrap up the investigation in a matter of several days to just a couple of weeks," he said, later adding that investigators could search for "months and months" and still not find all the at-risk cows.
Cattle contract BSE by eating feed containing material from other infected cattle. Eating meat products from infected cattle is believed to be the cause of variant Creutzfeldt-Jakob disease (vCJD), a fatal human disease similar to BSE.
DeHaven said the cows that remain untraced are not a "particular concern" for either public health or animal health. Very few cattle herds in the United Kingdom had more than one or two infected cows during the British BSE crisis, and thus it's unlikely that the Alberta herd had more than one or two infected animals, he said. Also, any cows that went to slaughter would have been condemned if they showed signs of neurologic disease, and current USDA rules bar all downer cattle from being processed for food, DeHaven said.
Agriculture Secretary Ann Veneman delivered the same message in testimony to the Senate Agriculture Committee yesterday. "Even in the case of those animals that are not found, we would not expect them to pose a significant risk to public health or animal health," she said in testimony posted on the USDA Web site.
As of Jan 26, the USDA had positively identified 28 of the 81 animals from the infected cow's birth herd that were sold into the United States in 2001. The agency will continue to follow any leads on cows other than the 25 born within a year before or after the infected cow, but they would be "of much lesser importance than the 25," DeHaven said.
In tracing the Alberta cattle to various other herds, investigators have examined those herds and picked out other cows that could have come from the Alberta herd, while eliminating others on the basis of their age or when they entered the present herd, DeHaven said. Cows that could have come from the birth herd have been sacrificed and tested for BSE. As of Jan 27, 227 cattle had been tested; 170 of the tests were negative, and results were still pending on the other 57, according to the USDA's online BSE updates.
After removing and testing cows that might have come from the Alberta herd, the USDA recently released hold orders on five herds in Washington and Oregon, DeHaven said. Those included the Mabton, Wash., herd where the sick cow last lived, plus herds in Mattawa, Wash.; Sunnyside, Wash.; Connell, Wash.; and Boardman, Ore. Herds still under hold orders are at Tenino, Quincy, Moxee, and Othello, all in Washington, and Burley, Idaho.
USDA officials at the news briefing rejected the idea of testing all cattle headed for Japan for BSE, saying it's scientifically unnecessary and too costly. Japan, which currently tests all its cattle for BSE, has stopped imports of US cattle since the BSE case.
David Hegwood, Veneman's senior advisor for international trade, said, "Some part of 90 percent of every animal slaughtered in the US is likely to end up in the Japanese marketwhich means we would have to test 90 percent of the cattle slaughtered for Japan. And a rough calculation of the cost of that is about $900 million." Since the total of US beef experts to Japan is about $1 billion a year, "it's just not worth it economically to go down that road," he said.
DeHaven said that testing animals younger than 30 months old would be at odds with science, because BSE has an incubation period of 3 to 8 years and very rarely is found in animals younger than 32 months. (USDA rules now require the removal of high-risk tissues such as the brain and spinal cord from carcasses of cattle older than 30 months, plus the removal of the small intestine from all carcasses. The prion proteins believed to cause BSE have not been found in muscle tissue.)
An international team of experts is reviewing the USDA's response to the BSE case and is expected to produce a report in about 2 weeks, DeHaven said in other comments.
Transcript of Jan 26 USDA news briefing
Agriculture Secretary Veneman's Jan 27 statement to the Senate Agriculture Committee
USDA's Jan 27 BSE update