American taste buds are changing, with exotic meats like bison and ostrich showing up on tables around the country. As part of this trend, elk meat is turning up in more butcher shops and restaurants. A malady similar to Mad Cow disease has elk ranchers on the alert.

At Herb's Quality Meats, customers line up to buy marinated chicken and premium beef. But demand for a specialty item is also brisk. "We sell tons of this elk meat," says Assistant Manager Mike Grass, adding that there's a reason elk meat is popular. "It's lean and it's rich, therefore, it's healthy. $21.99 a pound? this little piece of meat," he says. "Beef tenderloin's $19.99 a pound, but I prefer elk over beef. You can cut this with your fork, and it just melts in your mouth like butter."

American elk are big relatives of deer, a bull elk can weigh 500 kilograms. Hunters prize them as game animals, and the sight of a wild elk is always a highlight of any visit to a national park. But it's easier to see a herd on a ranch? since elk are a growing segment of the country's domestic livestock industry.

As president of the Colorado Elk Breeder's Association, Ron Walker takes pride in the 400 elk he runs on 14 hundred hectares of mountain land. None of them are wild. Like commercial herds throughout the United States, these animals are descended from elk that were captured years ago, and Mr. Walker says they maintain a dignity that other domesticated animals have lost. "The disposition and the majestic look of the animals, just the handling of 'em," he says. "You know, the products that they produce is so much different from raisin' beef cows cause if you got beef cows, you've got beef. That's all you've got. When we raise elk, we've got velvet antlers, we've got hard antlers, we've got breeding stock and we've got meat."

Elk's velvety springtime antlers can be cut off then powdered into health supplements. The hardened antlers that shed naturally in the autumn provide dramatic accents for home decoration. Then there are elk steaks, lean, tender and hormone-free. To meet growing consumer demand for these products, the number of Colorado elk ranches has tripled in the past decade, to more than 140. Mr. Walker estimates 16,000 elk are in these captive Colorado herds, with 170,000 animals nationwide.

But a mysterious disease could stop this industry in its tracks, as Colorado Division of Wildlife spokesperson Todd Malmsbury explains. "Chronic wasting disease has been found at least since the 1960s in a portion of northeastern Colorado and southeastern Wyoming," he says.

Chronic wasting disease, or CWD, afflicts less than 10 percent of wild deer and elk within this small region of the Rocky Mountains. Many scientists believe the deadly condition is caused by mutant prions, misshapen nerve proteins whose mysterious deformity spreads like a rot throughout an afflicted animal's nervous system. Experts aren't sure what causes the prions to deform in the first place, or exactly how the disease spreads from sick animals to healthy ones.

CWD causes pneumonia-like symptoms and brain decay. It's similar to Mad Cow disease, which worries health officials, since people who eat beef from infected cattle can die. There is no documented case of CWD in elk or deer ever making a human ill, or infecting other species.

Nevertheless, Mr. Malmsbury says the elk industry must work harder to avoid spreading CWD. "Unfortunately, there are some captive elk farms right now where animals, with the disease, have been transported unknowingly, not only to a number of sites in Colorado but to as many as 15 other states as well as Canadian provinces," he says. "So the disease is being transported through live animals that have been infected, to other places, in North America, that have never had the disease."

While most experts agree that Mad Cow disease spreads through contaminated cattle feed, and can be contained through better feeding practices, chronic wasting disease in elk and deer is harder to control. That's because it probably passes from one animal to another through saliva, urine and stool or even soil that a sick animal contaminated. CWD spreads slowly in the wild, but Mr. Malmsbury says it's more contagious in domestic herds. "Anytime you put animals in close proximity, a disease that's transmittable will be transmitted," he says. "It goes with a four-year-old in day care who has a cold, to elk and deer, put together in a pen, that have the disease."

In rare instances over the years, chronic wasting disease has infected commercial elk herds throughout North America. The problem has been dealt with in various ways. Occasionally, an entire herd has been quarantined or destroyed to prevent further contagion. But sometimes, the disease has been overlooked, since it may take more than 18 months before a seemingly healthy elk shows signs of CWD, and it's easy to misdiagnose without testing a dead elk's brain stem.

So it's not surprising that the transport of elk probably has spread the disease. To reduce the chance of shipping contaminated animals, Colorado has implemented better ways of tracking individual elk. Also, three years ago, Colorado became the first state to test every commercial elk carcass for chronic wasting disease. This is how the industry was able to confirm that five elk recently shipped from a Colorado ranch later came down with CWD.

To prevent further spread, at any ranch where an elk has tested positive, the rest of the herd may be destroyed. The federal government has set up a fund to reimburse ranchers who lose their animals this way. In addition, quarantine rules have been tightened statewide, and more stringent policies are being developed for commercial elk ranches outside of Colorado. Meanwhile, scientists nationwide are conducting tests to assure the ailment hasn't jumped the species barrier to cattle, other animals or people.

Thanks to this vigilance, butcher Mike Grass says the elk meat he sells is safe. "I haven't had any complaints," he says. "People are demanding it and eatin' it like crazy."