Health officials in the United States have been taking stringent precautions to prevent bovine spongiform encephalopathy (BSE). Imports of beef and bovine products are banned, and no one who has lived in the United Kingdom since the late 1980s, when the BSE epidemic first became known, is allowed to donate blood.
So far, no cases of BSE have been identified in US cattle, although the related diseases of scrapie in sheep and chronic wasting disease in elk and deer have been spreading. It is not known whether eating infected sheep, deer, or elk causes any form of Creutzfeldt-Jakob disease in humans, but the infectious agent—proteins called prions—have been shown to cross barriers between species.
Even though the US and UK governments banned the practice of feeding cattle products to cows in the early 1990s, some UK renderers continued to manufacture and ship contaminated meat and bone meal around the world. British export statistics, for example, show that 37 tonnes of "meals of meat or offal" that were "unfit for human consumption" were sent to the United States in 1997, well after the government banned imports of such risky meat. The ultimate use of these imports has not been identified.
Other beef byproducts that are still allowed to be imported into the United States include milk, blood, tallow, bone mineral extracts, collagen, semen, and serum albumin (used to make vaccines and medicines).
The Food and Drug Administration (FDA) told US drug manufacturers in December to stop using bovine serum from countries where BSE has been found, for making vaccines against flu, hepatitis A, diphtheria, pertussis, and tetanus, but vaccines already made from these materials are still being used.
An FDA committee will meet this month to discuss extending restrictions on who can donate blood to include people who lived in Europe for six or more months in the 1990s. The committee is also expected to discuss whether to ban donations from deer and elk hunters.
"We are doing our best to not be complacent," said Dr Linda Detwiler, a veterinarian with the animal and plant inspection service of the US Department of Agriculture. Referring to the emergence of unsuspected BSE in several European countries, she added, "We have tried to learn from their mistakes."
But Dr Tom Pringle, a biochemist in Eugene, Oregon, and an independent researcher on transmissable spongiform encephalopathies, said that US officials have not done enough to combat the disease. He said that the United States should set up a system to track bovine material coming into the country and increase testing.
Of the 900 million cattle in the United States, the agriculture department tested fewer than 12 000 sick cows for BSE in the last decade. None was found to have the disease. France, with 5.7 million cattle, is now testing 20 000 animals each week and identified 153 infected animals last year.