How the Cows Turned Mad

by Maxime Schwartz University of California Press, 2003; $24.95

English farmers first sounded the alarm in April 1985, when otherwise healthy cattle started acting edgy, showing random fear and aggression, and kicking their handlers. The afflicted animals also wavered as they walked, then lost their ability to stand, to lift their heads, and, eventually, to breathe. Postmortem inspection of their brains exposed a tangle of lesions that had turned once-solid gray matter into a spongelike mass. Bovine spongiform encephalopathy, or BSE, was its official name, but to a frightened, beef-loving public it became "mad cow disease."

The threat of mad cow disease, however, goes deeper than its monstrous effects on livestock or its economic impact on farmers. About a decade after the first cows went mad, ten cases of a new form of the degenerative brain disorder known as Creutzfeldt-Jakob disease (CJD) turned up in the U.K. CJD had been an extremely rare disease among people aged forty to sixty, but the average age of these newest victims was twenty-nine, and autopsies of their brains revealed lesions similar to the ones in diseased cattle. Just over a hundred deaths were reported from the new variant of CJD by 2001, and the evidence clearly suggests that the most likely cause is the consumption of beef.

Maxime Schwartz, a molecular biologist and now a professor at the Pasteur Institute in Paris (which he headed for a decade, from 1988 until 1999), has written a lucid and gripping account of these events in the context of the latest scientific research. "The Disease," as he prefers to call it, is actually one of several maladies similar in both cause and effect. In the mid-1700s, when it was first recognized in sheep, The Disease was called scrapie, because suffering animals tended to rub their skins raw. By the 1900s scrapie was recognized as infectious, but unlike viral or bacterial diseases, it seemed to produce neither a fever nor an immune-system response. Moreover, healthy sheep inoculated with tissue from animals with scrapie took years to develop symptoms, far longer than for any other known infection.

In the 1950s a similar disease was recognized in people: kuru, a wasting of the brain found among the Fore people of New Guinea, appeared to be transmitted by their traditional habit of eating deceased (and diseased) family members. Like scrapie, it was slow to manifest itself, and also like scrapie, it led to no immune response. Its symptoms resembled those of Creutzfeldt-Jakob disease, but since no CJD sufferers were ritual cannibals, the connection between kuru and CJD was unclear.

Around the time the mad cows first staggered onto the scene, Stanley Prusiner, a microbiologist at the University of California, San Francisco, suggested that both diseases were caused by a new kind of infectious agent that was neither a virus nor a bacterium. He named it a "prion," and identified it with a nondescript protein that normally occurs in many mammals, including people. Although prion molecules do not incorporate DNA, and thus cannot reproduce by conventional means, mutant forms do have a primitive ability to induce identical imperfections in healthy prions. Schwartz calls it the molecular "kiss of death." The process leads to a growing accumulation of bad prions that eventually destroy nerve cells in the brain. At first Prusiner's idea was controversial, but biologists have gradually come to accept it, and in 1997 Prusiner won a Nobel Prize for his work.

Thanks to vigorous public-health measures, including a ban on feeding animal tissue to livestock, mad cow disease seems to be on the wane. But prion disease remains frightening. Because it takes years for its symptons to develop, Schwartz cautions, the extent of cow-induced infection in people may not be known for another generation. Nor can we assume that BSE is the ultimate prion infection. Suppose "The Disease" morphs into a form that causes few symptoms in animals but moves much more readily than BSE from livestock to people? Then even Ronald McDonald might decide to become a vegetarian.

Laurence A. Marschall, author of The Supernova Story, is the WK. T Sahm professor of physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.

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