It will be a while yet before science has much to offer victims of the variant of Creuztfeldt-Jakob disease that has been linked to consumption of beef tainted with bovine spongiform encephalopathy (mad-cow disease). The prospects might be better if the culprit were a virus or a bacterium, but it happens to be a strange molecule called a prion, a wholly new class of infectious agent that was discovered by Stanley Prusiner in the 1980s (he won the Nobel prize for it in 1997) just as mad-cow disease began making headlines. “We don’t have a treatment, and there is no possibility of a treatment in the near future,” says Martin Ziedler, a CJD expert who has consulted for the World Health Organization.

For the moment, scientists are still studying prions with wide-eyed wonder. Perhaps the oddest thing about prions is that they are so close to being ordinary. As far as scientists know, prions are almost identical to proteins found in humans and cows and almost every other living thing. Proteins are the whole point of DNA molecules: DNA is a set of instructions that a cell uses to manufacture the proteins it needs for carrying out the things it must do to live. A protein is made up of hundreds of amino acids strung together into a snakelike molecule so long that it tends to fold up like an impossibly intricate origami sculpture. Protein folding is currently the subject of intense research because it plays an important role in determining how proteins work in the body. Some scientists now think that a prion is nothing more than a specific protein that folds in an abnormal way: think of two identical pieces of paper, one folded into a paper airplane and the other crushed into a ball.

This odd folding may be what gives prions their unique characteristics. When a prion comes in contact with its normal protein counterpart, which is particularly abundant in the brain, the protein folds like a prion–becoming, in effect, a prion itself. In the process, the newly formed prions gain a kind of omnipotence. For reasons scientists don’t yet understand, the body cannot break prions down the way it can normal proteins: once prions make their way into nerve tissue and begin spreading, there’s no stopping them. Entering first through the stomach, prions travel through the body’s network of nerve cells to the brain. Slowly at first, and then with increasing speed, they turn the victim’s brain into a spongy mass of useless tissue (chart).

What makes prions particularly difficult to work with is that they have no DNA, which means scientists have to develop a new set of tools for studying them in the lab. Prions also don’t behave like viruses or bacteria, which tend to replicate quickly and make their presence known. CJD symptoms don’t appear for 10 years, and perhaps for as many as 40. Because the incubation period is unknown, scientists don’t yet have a handle on how many people may eventually come down with the disease: estimates range from hundreds to millions. Dosage may make a big difference. If you ingest a lot of prions, chances are the disease will surface more quickly than if you had just a few.

Dosage, in fact, may have played a key role in triggering the BSE epidemic in the first place. Back in the 1980s British scientists thought cattle caught BSE when they were fed the remains of sheep infected with scrapie, another brain-wasting illness. It quickly became clear that BSE was a completely different disease–one that more easily jumps from one species to another (humans have never contracted scrapie). By the late 1990s, after the British outbreak peaked, scientists began to suspect that the BSE prion had arisen spontaneously in a single cow in the early 1970s. Remains of this infected cow were then fed to other cattle, which in turn were fed to still more cattle and so on. All the while, prions multiplied. BSE prions might never have spread to humans had they not been circulated among cattle for decades before. Eventually prions became so numerous in British beef that they had no problem “crossing the species barrier,” as scientists say.

The cow-origin theory has been endorsed by the British government’s recent report on the BSE crisis, but some scientists are already beginning to cool on it. Experimental efforts to replicate the spontaneous formation of BSE prions in cows have failed. BSE prions have also proved particularly adept at species jumping: they’ve already shown up in cats, and scientists have succeeding in infecting other animals in the lab. Analyses of the BSE prion also show that it changes very little from one species to another, leading some scientists to conclude that “BSE may be a kind of superstrain” of brain-wasting diseases, says Priola. If she’s correct, current livestock-feeding regulations would be woefully inadequate. Although some countries including the United States have both banned the feeding of cattle remains to cattle, they still allow farmers to feed cattle to sheep and pigs, and vice versa.

Despite the slow start scientists are not completely without hope. The Rocky Mountain lab, for instance, has identified several compounds that appear to inhibit the formation of BSE prions. They might prove useful for treating victims in the early stages of CJD, but at present there’s no diagnostic test; scientists need to take tissue samples of the brain, tonsils or appendix, where prions tend to congregate. Scientists at Zurich University in Switzerland say they have come up with a more convenient and accurate test, but it may be years before it is widely available. For now it’s a tortoise race between prions and scientific research.