Agriculture officials in Washington say they have received preliminary independent confirmation from the UK that the United States has its first case of BSE.
The news came as investigators battled to trace the path the infected cow took from birth to slaughter.
Scientists at the Veterinary Laboratories Agency in Weybridge, Surrey concur with the assessment of tests on the Holstein cow that led US officials to conclude the nimal had the brain-wasting disease, said US Agriculture Department spokeswoman Alisa Harrison.
"We are considering this confirmation," she said, adding that the British laboratory would still conduct its own test using another sample from the cow's brain. Final test results on the cow from Washington state were expected by the end of the week.
Meanwhile, Ms Harrison said, investigators were working through the Christmas holiday to prevent a potential outbreak of the deadly disease and calm public fears about the United States' food supply.
Government and cattle industry officials voiced assurances that the beef on American tables was safe to eat.
"The risk to human life is extremely low," Agriculture Secretary Ann Veneman said.
But the biggest buyers of US beef around the world slapped bans on imports, and there were increasing doubts among the US population, which each consumes an average of nearly 65lb of beef a year.
PA