Washington - American health officials were scrambling Friday to trace the first case of mad cow disease in the United States to its source, after a British veterinary laboratory confirmed that the infected cow had bovine spongiform encephalopathy (BSE).
Brain specimens from the Holstein dairy cow from a meat packing firm in the north-western state of Washington, tested positive for BSE at a USDA lab in Iowa.
But the USDA sent specimens to a veterinary lab in Britain for confirmation, since Britain has had far more experience with the disease.
"The test samples were received at the laboratory in Weybridge, England, early Christmas morning," the US department of agriculture said on Thursday in a statement.
"The United Kingdom veterinary pathologists concur with our interpretation of the December 22 positive test conducted by USDA pathologists at the National Veterinary Services Laboratory in Ames, Iowa," it said.
The statement said USDA chief veterinarian Ron DeHaven "considers this concurrence to be confirmatory of our finding of a positive BSE case."
"The Weybridge lab will conduct a series of additional confirmatory tests," it said, "and we anticipate they will be consistent with the earlier findings."
At least 26 countries, including top importers Mexico and Japan, have now barred US beef imports, a massive blow to the multi-billion-dollar industry that directly employs one million people.
Domestic cattle prices and fast food industry shares have taken a beating in the wake of the scare, and activists launched appeals for tougher food safety standards.
Government officials promised Americans their holiday beef was safe, saying the mad cow case unearthed in Washington state posed a negligible health threat.
As of 0730 GMT on Friday, Australia, Brazil, Canada, Chile, China, Colombia, Costa Rica, Hong Kong, Indonesia, Japan, Jordan, Malaysia, Mexico, Panama, Paraguay, Peru, Russia, Singapore, South Africa, South Korea, Taiwan, Thailand, Trinidad and Tobago, Turkey, the United Arab Emirates and Vietnam had all halted US beef imports.
US Agriculture Secretary Ann Veneman said authorities were doing all they could to protect consumers and that as the spinal cord and brain of the infected cow had not entered the food chain, the impact of the case should be isolated.
The US beef industry, hoping to avoid the fate of its European counterpart which was savaged by the disease, mobilised to stop further potential cases entering the food chain.
Meat processing firm Vern's Moses Lake Meats, of Moses Lake, Washington state, has recalled about 20 beef carcasses that may have been exposed to raw tissue containing BSE.
And the farm where the four-and-a-half-year old infected cow was kept before slaughter put its remaining 4 000 head of cattle in quarantine.
The Washington Post on Friday quoted a veterinarian familiar with the investigation saying that the infected animal may have brought the disease from another US state or even from outside the country, possibly from Canada.
USDA officials were retracing the life of the infected cow to find the possible source of the disease in order to identify all possible contaminated animals and meat products.
Officials said one of two herds in Washington state was the birth herd of the infected animal, but DeHaven said investigators were "tracing back further from there."
The veterinarian, who requested anonymity told the Post that the infected cow had not spent her entire life in Washington state, adding that large number of cattle had been imported in recent years into that state from Canada.
The only previous outbreak of mad cow disease in North America was a single case at a farm in Alberta, Canada, in May. The United States has since imposed a ban on Canadian cattle and products.
DeHaven declined to speculate on whether the animal came from Canada, but noted that the Holstein probably ate contaminated feed in 1999 or 2000, well before the Canadian mad cow case was discovered.
Activist groups called on Washington to impose tougher standards to ensure the safety of the food supply. Michael Hansen, with the advocacy group Consumers Union, said the United States should adopt the same stringent testing as Europe and Japan.
Although 37 million cows were slaughtered here last year, only 20 000 were tested for mad cow disease, fewer than France tests each month. "For us to recover our export market, they are going to have to do more extensive testing," Hansen said.
The New York Times said on Friday that the USDA was considering adopting more rigurous screening methods such as those used by Europe and Japan, and changing the way meat from suspect animals is used.
Some food safety experts, the daily said, favor adopting Britain's ban on selling brains or vertebrae or meat attached to them, as well as its mandatory testing of all cattle over 30 months old and tagging of all cattle from birth to slaughter.
Mad cow disease has been linked to a form of the fatal brain-wasting Creutzfeldt-Jakob disease that affects humans. - Sapa-AFP