“The risk of getting aplastic anemia that is posed by consuming a horsemeat burger is very low indeed,” Lees said.
Nonetheless, the development heightened concerns about the security of Europe’s food system.
Authorities across the continent are testing thousands of meat products for the drug, and for horse DNA, after horsemeat was found in food products labeled as beef in several countries.
Food Standards Agency head Catherine Brown said that before the current crisis, the agency had tested about 5 percent of the horses slaughtered in Britain _ and about 6 percent of those had shown traces of bute.
“That would say there has been a significant amount of carcasses with bute in going into the food chain for some time,” she said.
Pan-European police agency Europol is coordinating a continent-wide fraud investigation amid allegations of an international criminal conspiracy to substitute horse for more expensive beef.
The scandal has uncovered the labyrinthine workings of the global food industry, where meat from a Romanian slaughterhouse can end up in British lasagna by way of companies in Luxembourg and France.
It has also raised the uncomfortable idea that Europeans may unwittingly have been consuming racehorses, which are often treated with bute.
Britain’s Food Standards Agency said it had begun testing all horses slaughtered in Britain for bute, and that none would be exported for consumption unless they tested negative. The agency previously tested only a small percentage of slaughtered animals, which has fueled criticism of its failure to catch the horsemeat contamination sooner.
Almost no horsemeat is consumed in Britain, where hippophagy _ eating horses _ is widely considered taboo. But thousands of horses killed in the country each year are exported for meat to countries including France and Belgium, which have a culture of eating horsemeat.
A “horse passport” system, which records whether animals have been treated with bute, is meant to stop the drug entering the human food chain.
On Thursday, Britain’s Aintree race track said a slaughterhouse in northern England shut down this week by government investigators had a contract to dispose of fatally injured racehorses.
The racecourse said it was “as confident as we possibly can be” that none of the meat had entered the human food chain.
The trail of illicit horsemeat stretching across Europe spread still further Thursday when Rangeland Foods, a processing factory in Ireland, said it had withdrawn some batches of burger products which contained beef supplied from Poland after it tested positive for up to 30 percent horse meat.
Food Safety Authority of Ireland said the products had been sold to the catering and wholesale sectors and distributed to Ireland, Britain, Spain, France, Germany and the Netherlands.