Safe Food_ Bacteria, Biotechnology, and Bioterrorism - Marion Nestle [150]
The new method killed most bacteria and viruses. It did not, however, inactivate prions, a generic term for the highly unusual infectious agents believed to cause a disease called scrapie in sheep and related diseases in other animals. These invariably fatal diseases affect the brain and nervous system; they are called spongiform encephalopathies because they cause sponge-like holes in the brains of animals and people. Prion diseases present fascinating biological problems. They appear to involve transmission via proteins (rather than bacteria, viruses, or DNA), as well as “species jumps” from one kind of animal to another. In the era before mad cow disease, prion diseases seemed to be confined to their particular host animal. Scrapie, for example, affected sheep in Britain for at least three centuries but did not bother people. Instead, people exhibited their own specific and rare form of the disease, as did cows; both appeared spontaneously and were considered “sporadic.” At this point, we need to know the names of these diseases: scrapie in sheep, bovine spongiform encephalopathy (BSE) in cows, and Creutzfeldt-Jakob Disease (CJD) in people.4 Because of the way sick cows behave, BSE soon became known as mad cow disease. In turn, mad cow disease soon emerged as the link between prion diseases in sheep and in people.5
BSE first appeared soon after cows ate the inadequately rendered meat-and-bone meal supplements. These supplements almost certainly contained offal from sheep infected with scrapie; Great Britain raises far more sheep than cattle, and scrapie is common in British sheep. Later, they surely also contained offal from cows with as yet unrecognized BSE. Veterinarians observed the first case of BSE in a cow in 1984 and confirmed the disease in 1985. During the next few years, the number of BSE cases in cows increased, signaling a growing epidemic. In 1988, an investigating committee deduced that the sheep disease must have jumped to cows. At this point, the British government banned the use of offal in cow feed and required farmers to report BSE cases and to destroy suspect cattle, all the while repeatedly reassuring the public that British beef posed no health risk.
Despite the new regulations, government officials promised support to the beef industry. The prime minister, John Major, said he was “absolutely determined to reduce the burden of regulation on business.”6 Although the government vehemently denied it, beef producers often ignored the 1988 feed ban and nearly half of all the BSE cases occurred in cows born after that year. In 1990, the government appointed yet another BSE review committee, but, according to a later investigation, pressured its members to declare beef safe to eat. Meanwhile, cases of BSE in cows continued to rise, reaching a peak in 1993 and then declining gradually as the use of rendered meat-and-bone meal ceased. During the next few years, scientists became increasingly convinced that mad cow disease might be transmitted to people. Britain banned the use in human food of mechanically recovered meat from cow vertebrae (lest it be contaminated with brain or nervous tissue), but health officials continued to deny any risk from this practice. The European Union, however, banned the sale of British beef for three years, noting that the disease seemed to be a particularly British problem.7
These actions came much too late. In 1996, British doctors identified ten young people with a previously unknown variant of Creutzfeldt-Jakob