Disease is wasting the West's wild herds

  • The brain, riddled with holes, of a deer that died ofCWD

    Univ. of Wyoming photo

Nobody knows where the disease came from, or if it has existed forever, confined to the lodgepole forests, shortgrass prairies and alfalfa fields of north-central Colorado and southeast Wyoming. It is not known how it passes among its victims. What is certain is that the whitetails, mule deer and elk that contract it inevitably die after a prolonged period of suffering - staggering, listlessness, progressive emaciation. Researchers call it chronic wasting disease, or CWD (HCN, 3/16/98).

Since it first appeared in captive mule deer at a Colorado Department of Wildlife research lab near Fort Collins in 1967, it has been an ugly regional phenomenon, killing a small percentage of the wild elk and deer within its range. Only about 100 cases of chronic wasting disease have been documented in wild mule deer since 1981. The disease is still rare, but it is spreading slowly.

In the past two years, CWD has spread to a new niche - the expanding game-farm industry, where elk and deer are ranched for meat, velvet antlers and captive trophy shoots. The brisk interstate commerce in elk breeding stock and bull elk sold for the trophy shoots has brought the disease to game farms in Nebraska, South Dakota, Oklahoma and Saskatchewan, Canada.

Chronic wasting disease is a transmissible spongiform encephalopathy, or TSE, similar both to scrapie, a disease that for centuries has periodically devastated domestic sheep herds, and to the "mad cow" disease that wreaked havoc on the British beef industry in the early 1990s. It is also linked to an extremely rare disease that affects humans, a variant known as Creutzfeldt-Jacob disease. Under a microscope, brain tissue from TSE-infected animals shows the sponge-like degeneration that gives the disease its name, but the infection attacks no other organs and triggers no response from the animal's immune system. Scientists have no way to test living animals for the disease - it's diagnosed by analyzing the brain tissue in dead animals.

"Without a live test, we have no way of knowing what our rate of infection is," says Tom Cline, a vet with the South Dakota Animal Husbandry Board. "Could be zero, could be 100 percent. We're not even sure how long it takes to show up." In South Dakota, 300 of the state's 2,000 captive elk are under quarantine for chronic wasting disease.

Why is chronic wasting disease more prevalent among confined animals than in the wild? Cline explains, "Let's face it, captives stay around longer, they have much more contact, and they have a much greater chance to pass the disease around. If a mule deer is staggering around in the wild, a predator will just take it down, probably before it has a chance to pass the disease on."

A recent example

In May of 1999, two elk that died on a newly established Oklahoma game farm were diagnosed with chronic wasting disease, and the farm was placed under a five-year quarantine. The infected herd had been purchased almost two years before from the Kesler Game Farm of Philipsburg, Mont. Neither Oklahoma nor Montana will admit that the elk were exposed to the disease in their state. Until this incident, both states were considered free of the disease.

Gene Eskew, a vet for the Oklahoma Department of Agriculture, says, "Based on the known incubation periods for this disease, we believe those elk were exposed before they got to our state. Exactly where is hard to say. That Montana herd was from a wide, wide variety of sources."

The possibility that game farm animals could pass chronic wasting disease on to wild animals outside the fences has long worried researchers, game managers and wildlife advocates. Mike Miller, veterinarian for the Colorado Division of Wildlife, has researched the disease since its discovery.

"The area where CWD is found in the wild has low numbers of elk and mule deer," he says, "and the disease has been slow to spread for that reason. If infected animals were brought into the western part of Colorado, where our game herds are much larger, it would be a disaster."

Miller says that when it comes to trying to manage CWD in wild herds, the alternatives are "hell if you do, hell if you don't. This is not like the bison/brucellosis problem in Montana, where you have vaccines and tests to help you. About the only way we know to manage CWD is to do a density reduction on the animals that may be carrying it, which basically means clobbering the native wildlife."

The Colorado Division of Wildlife asked for a moratorium on new game farms in the part of the state where the disease is found in wild herds, but its request has gone unheeded. The Department of Livestock continues to license elk farms there.

Wyoming veterinary pathologist Beth Williams, one of the pioneers in chronic wasting disease research, says, "I have always been worried that this disease would eventually get into the game farms and be moved around that way."

Chris Marchion of the Montana Wildlife Federation puts it more bluntly: "You can document every single instance of CWD travel and trace it back to a game farm," he says. "We need a legitimate moratorium on transporting game-farm animals until we get a live test, or some kind of effective monitoring. All we have done so far is provide this disease with the best possible means of transportation."

"In one sense, we pose a bigger risk because we move animals," says Paonia, Colo.-based Steve Wolcott of the Elk Research Council, a game-farm trade group. "But wherever they go, they're behind a fence."

He adds that quarantines and close monitoring should control the spread of the disease. In Colorado, for instance, state regulators record the deaths and sales of all captive elk, and all deaths are examined for chronic wasting disease. The Elk Research Council has contributed more than $180,000 to researchers studying the disease, says Wolcott.

"The critics of the elk industry are not asking the state wildlife agencies to commit to eliminating the disease in the wild herds," says Wolcott. "Yet, the game farmers are being asked to bear responsibility for the spread of the disease.

"We will bear some cost and pain to get rid of the disease," he says. "At the same time, we're not going to put ourselves out of business."

Wyoming fought a lengthy and costly court battle to outlaw the practice of game farming altogether, as did California. Washington, Oregon, Nevada, Arizona and Alaska have outlawed captive trophy shooting. Colorado leads the West in the number of licensed game farms operating, with 155 scattered throughout the state.

Larger questions loom

Wildlife concerns aside, the possibility that chronic wasting disease can be transmitted to traditional livestock, or even humans, worries many researchers. Experimental attempts at infecting cattle with the disease at several research facilities have so far failed or proved inconclusive, but it is still too early to tell. Bruce Chesebro, of Rocky Mountain Laboratories in Hamilton, Mont., is an expert on TSE diseases and has followed chronic wasting disease with growing alarm.

"Somebody at the Montana Department of Livestock needs to be very worried about the spread of this disease to the cattle industry," Chesebro says. "Elk and deer are closely related to cattle, and CWD has already made at least one shift, from mule deer to elk. Scrapie moves from sheep to goats with no problem. Who is to say that CWD cannot make the shift to cattle?"

Chesebro was in England during the mad cow epidemic, and witnessed firsthand the collapse of the beef industry there. "Because TSE did affect human beings there, the emotional reaction was tremendous. If we get even one case of CWD in Montana cattle, the industry will be in deep trouble."

Mike Miller points out that scrapie has never passed to humans or cattle, despite a long history of close contact. "All our data so far say CWD cannot pass to cattle. That is not to say that it cannot happen. I just believe that this is a serious enough problem with respect to our wildlife resources without raising the issues of transmission to humans or cattle."

Hal Herring writes and hunts from Corvallis, Montana.

You can contact ...

* Steve Wolcott, Elk Research Council, 970/527-4586.

* Mike Miller, c/o Colorado Division of Wildlife, 317 W. Prospect, Fort Collins, CO 80526 (970/472-4300).

* Chris Marchion, Montana Wildlife Federation, 2105 Garfield, Anaconda, MT 59711 (406/563-6145).

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