Since the closing of many countries to US beef exports in 2003, the country had managed to recover access to 82 per cent of its former markets, originally worth about $3.9 billion a year.
Japan, the largest market for US beef exports, had only resumed imports from the US in December after a ban was imposed in May 2003. The country suspended imports in January this year after the country's inspectors found banned cattle backbone material in three of 41 boxes in a shipment.
The new BSE case could push the country to extend the suspension.
The US secretary of agriculture, Mike Johanns, said yesterday that samples taken from a non-ambulatory animal on a farm in Alabama showed it had BSE. The animal was buried on the farm and it did not enter the animal or human food chains.
Based on initial information it was an older animal, quite possibly upwards of 10 years of age, indicating it would have been born prior to the implementation of the Food and Drug Administration's 1997 feed ban, he told reporters. Older animals are more likely to have been exposed to contaminated feed circulating before the FDA's 1997 ban on ruminant-to-ruminant feeding practices, which scientific research has indicated is the most likely route for BSE transmission.
Clark Clifford, chief veterinary medical officer at the US Department of Agriculture (USDA) also said it was too early to determine whether the animal was of US or Canadian origin.
Since June 2004, all sectors of the cattle industry have been required to submit samples from about 650,000 animals from the highest risk populations and 20,000 from clinically normal, older animals, as part of the USDA's BSE surveillance program.
The current incident is the second animal to have tested positive under the program, and the third to have been found in the US.
Asked by a reporter if the second case would impact ongoing negotiations to open up the Japanese import beef market, Clifford said the US has a number of safeguards to insure its beef imports are safe. Japan has itself reported about 20 cases of BSE.
South Korea had announced prior to the result that a positive test result would shut down the scheduled reopening of its market early next month. Under the agreement reached with the US, that country reserved the right to close its market again if any more cases of BSE were discovered.
Earlier this month the discovery of a piece of bone in a shipment from Swift & Company to Hong Kong led the Chinese territory to ban beef from the company last week.
After the discovery of a BSE-infected cow in the US in 2003, $4.8 billion worth of beef and beef product exports were banned. Markets accounting for $3.8 billion have since been recovered.
On 7 March Malaysia became the latest country to open its market to US beef products. In January Taiwan reopened its markets to US beef.
In 2003, the US exported about $76 million worth of beef to Taiwan, with boneless beef products accounting for $56 million.
Taiwan reopened its market to U.S. beef in April 2005, but closed it again in June following the confirmation of a second US case of BSE.
Japan was the largest importer of US beef prior to 2003, buying up $1.4 billion worth of the meat a year.
Johanns reported he had met with the Japanese minister of agriculture, forestry and fisheries, Shoichi Nakagawa, in London on March 10 to discuss dropping the suspension on US beef. The USDA produced a detailed report on how banned cattle backbone material had turned up in beef shipped to Japan in January.
The USDA report said the mistake was due to poor procedures at two meat packing plants and a lack of training for USDA inspectors.
"I indicated to minister Nakagawa that we received their questions and we are in the process of completing the responses," Johanns stated. "I also indicated that we anticipate submitting those responses to Japan next week."
The second US case of BSE was detected in November 2004 in an animal born and raised on a ranch in Texas. The animal was born prior to the implementation of the 1997 feed ban. The animal was dead upon arrival at the packing plant and was then shipped to a pet food plant where it was sampled for BSE. The pet food plant did not use the animal in its product, and the carcass was destroyed in November 2004.
BSE or mad cow disease can lead to its variant, Creutzfeldt-Jakob Disease (vCJD), in humans. It is spread by prions, abnormally shaped proteins that originate in the neurological tissues.
BSE spreads by consumption of feed that has been contaminated by prions. The human form of the disease can be transmitted if a human being eats BSE infected meat, and through blood transfusions.
Consuming meat from infected cattle has led to the deaths of 154 people worldwide from vCJD.