The first symptoms don't look like much. People get listless, moody, sometimes scruffy. Then they start to walk strangely, stumble a lot as if drunk, and finally end up in a wheelchair. Soon they can't remember words, faces, loved ones. By the end--which usually comes after a few years--patients are demented and mute. No cure is known.

           Until recently, Creutzfeldt-Jakob Disease (CJD) was one of those rare conditions known mostly to medical specialists; one in a million people, the statistics said, would get it, and generally in old age. That's why doctors in England couldn't figure out what was going on over the last 10 years, when patients in their teens, 20s, and 30s started showing up. Their symptoms weren't quite like the classical form of the disease; they died faster, too, often within a year. And their brains, when cut open after death--the only sure way to diagnose CJD--showed an unusual pattern. They had turned into a kind of sponge, full of holes surrounded by soft masses of dead cells. What they looked like, oddly enough, were the brains of cows killed by "mad cow disease," a new condition that was giving English beef farmers no end of trouble.

           You've probably heard the next part of the story. For 10 years, government officials and most scientists in Britain and elsewhere denied any connection between mad cow and the new type of Creutzfeldt-Jakob, and they set up a scientific commission to prove the point. But when the commission delivered its report this spring, it instead dropped a bombshell. "On current data and in the absence of any credible alternative," it announced, "the most likely explanation at present is that these cases [of the new form of CJD] are linked to exposure to" mad cow disease.

           So far, it might all have been an interesting tale from the other side of the Atlantic. No British beef has been imported to the U.S. since 1985, and U.S. officials have always insisted that there is no mad cow disease in this country. Beef producers and processors--who see the fate of a $60-billion-plus industry hanging in the balance--said the same.

           But while the headlines have dutifully faded, some disturbing evidence continues to trickle in. There have been more of the strange CJD cases in Britain, and one in France. There is now stronger evidence of a potential link between human and cow disease. And it's become clear that while the U.S. doesn't have the British version of mad cow, something very odd is going on with American cattle.

           The best-case scenario, according to the experts, is that the whole thing will blow over as another food scare. The worst is an epidemic that, as one advocate put it, "makes AIDS look like the common cold." For now, U.S. policy is to bet on the former, and to reject the kinds of precautions Britain reluctantly put in place years ago. But behind the scenes there's an increasingly heated argument with high stakes in science, money, and politics. How it turns out will depend in part on what researchers, especially at large agriculture universities like Minnesota and Wisconsin, find in the next few years--and, for that matter, whether they even look.

           The scientific name for mad cow disease is Bovine Spongiform Encephalopathy (BSE), which roughly translates as "cow's spongy brain disease." It's part of a larger group of "transmissible spongiform encephalopathies" (TSEs) that show up in various species--cats, cows, humans, and so on. One of the most common is scrapie, which has been killing sheep in Europe and North America for decades.

           BSE is a more recent arrival. Few if any cases were documented until 1985, when vets were called to Ashford, England to check on some cows that had taken to leaving the herd, stumbling a lot, and occasionally running around like maniacs. By the time the vets and the press had put a name to the new disease, several hundred new cases were being diagnosed each week. By early this year, close to 200,000 BSE cows had been diagnosed, killed, and incinerated in the U.K.

           To this day, no one knows exactly how spongiform encephalopathies are transmitted, or for that matter by what; from what scientists have learned so far, the "agent" in question may be so radically new they're not even sure it exists. It is, research suggests, not a bacteria, virus, or parasite, but a protein molecule run amok. The warped chain of amino acids known as a "prion" can wrap itself around other proteins, preferably in the brain and central nervous system, causing them to also warp and attack other proteins, ad infinitum. Eventually whole clusters of cells die, leaving the spongy pattern typical of TSEs.

           Prions have a couple of other interesting properties. They appear resistant to sterilization, heating, freezing, drying, even toxic chemicals. And they're infectious: When you inject brain tissue from a TSE animal into another, you usually create a form of the disease. That's how thousands of dwarves, who for several decades received growth hormone from dead people's pituitary glands, came down with the human spongiform encephalopathy, Creutzfeldt-Jakob. Today, human growth hormone is made in the lab, but plenty of other uses of cadaver brain parts remain: Neurosurgeons sometimes use outer-brain membranes from dead people, and pituitary hormones have been used as a treatment for female infertility.

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