Britain remains in the grip of mad-cow hysteria two weeks after the government conceded that eating afflicted cows-the formal name for their ailment is bovine spongiform encephalopathy, or BSE–might possibly cause the human brain disease CJD. The British government is considering killing 4.5 mill/on older cattle that could harbor BSE, and British fast-food restaurants and airlines stopped serving burgers made from homegrown cows. The European Union last week banned exports of British beef and beef products for at least six weeks. Most ominous, the Health Ministry announced the latest in a series of CJD deaths that are so different from the textbook description of the disease-the victims were young, the brain tissue looked like Alzheimer’s–that they suggest a link to mad cow, says Dr. Paul Brown of the U.S. National Institutes of Health. There have now been 11 suspicious CJD deaths in the last two years. In the United States, activists are filing a suit this week demanding that the Food and Drug Administration ban a practice suspected of causing mad-cow disease in Britain: feeding cattle the rendered parts of cows and sheep. “Eventually this practice is going to get us into trouble,” warns virologist Richard Marsh of the University of Wisconsin. “We will be in the same quagmire as Great Britain.”
At first glance, the risk of getting CJD from cows, mad or otherwise, in the United States seems minimal. The U.S. banned imports of British beef in 1989, three years after BSE was identified in British herds. Since then the Agriculture Department has autopsied more than 8,000 cows without turning up a single case of mad-cow disease. Yet American farmers routinely feed rendered sheep and cattle to their cows, just as the British did until scientists began suspecting that herds were getting BSE from sheep that had scrapie, another brain-rotting disease; the practice was banned in 1988. Six years later the U.S. FDA proposed a ban on using sheep offal as cattle feed, but vehement protests from the rendering and livestock industries blocked it. Last week the FDA promised a ban “any day now.” But such a prohibition would not affect cattle cannibalism: some 14 percent (by weight) of the cow carcasses rendered in the U.S. are fed to other cattle, according to the USDA. And a 1985 outbreak of encephalopathy among ranched mink in Wisconsin, says Marsh, was traced to diseased cows that had been turned into mink food.
The United States has already had one surprise outbreak of CJD. Between 1965 and 1985, more than 8,100 children afflicted with dwarfism were injected with growth hormone derived from the pituitary glands of human cadavers. In 1985, three of the recipients came down with Creutzfeldt-Jakob. Suspecting that one or more of the pituitaries had come from a CJD victim, the FDA banned the use of cadavers as sources of growth hormone. (Now the hormone is synthesized genetically.) So far, 15 American dwarfism patients and an additional 80 overseas have contracted CJD from cadavers infected with the disease.
Scientists could better gauge the risk of contracting mad cow and Creutzfeldt-Jakob ff they knew what caused them. But no virus or bacterium has ever been associated with the diseases. Suspicion has therefore fallen on an infectious protein, or prion. According to a theory advanced by neurologist Stanley Prusiner of the University of California, San Francisco, in 1982, prions are misshapen molecules that wrap themselves around normal proteins in brain cells (diagram). This deadly embrace transforms the healthy proteins into more misshapen prions. They, in a lethal chain reaction, alter still more healthy proteins. The change in shape makes the proteins invulnerable to enzymes that would normally break them down. The proteins accumulate, eventually forming the clumps and holes characteristic of Creutzfeldt-Jakob. And prions from one species can sometimes infect the brains of another.
Although the British press is carrying predictions that 500,000 beefeaters a year could die of CJD associated with mad-cow disease, in fact it is very hard to contract any of the brain-rotting ailments. For one thing, there are hints that you need to be genetically susceptible. Thousands of patients who received infected growth hormone did not get CJD; those who did had a particular kind of brain-protein gene. Also, UCSF’s Fred Cohen points out, a prion can alter healthy brain proteins only if it resembles them: “The fit between the human brain protein and the bovine prion is not very good.” The question is whether it was good enough to kill at least 11 people in Britain.
Since no virus or bacterium has ever been linked to Creutzfeldt-Jakob disease, scientists suspect an infectious protein, called prion, is the culprit.
1 A pathological prion comes in contact with a healthy protein in the brain, causing it to change shape
2 The altered protein changes additional proteins, which attack still more, in a chain reaction
3 The altered proteins accumulate, and cause brain tissue to clump, leaving gaps
Diseased tissue: In Creutzfeldt-Jakob disease, the brain is riddled with holes
