Is chronic wasting disease the new mad cow?

What to eat. What not to eat.
Feb. 26 2004 9:20 AM

Oh, Deer

Is chronic wasting disease the new mad cow?

Illustration by Nina Frenkel

These days, every disease has its animal mascot: There's the civet for SARS, the chicken for the avian flu, the prairie dog for monkeypox, and, of course, the cow for mad cow disease (also known as bovine spongiform encephalopathy). But there's another unlucky animal whose disease has gotten a lot less play in the national press. Unless you live in an affected state, like Colorado, Wyoming, or Wisconsin, you probably haven't heard much about chronic wasting disease, or CWD—in essence "mad deer disease"—which is afflicting deer and elk populations (both wild and farmed) in the West and Midwest and is spreading at a much faster rate in this country than its bovine counterpart. (For a map of the affected regions, click here.)

CWD, like bovine spongiform encephalopathy and its human equivalent, variant Creutzfeldt-Jakob disease, or vCJD, is known as a transmissible spongiform encephalopathy. Like other TSEs, CWD is believed to be caused by misshapen prion proteins that gradually take the place of normal proteins and destroy brain cells, causing large holes to form in the brain. TSE victims are left emaciated, stumbling, drooling—and, inevitably, dead. But there is no confirmed theory of how CWD is spread, as there is for BSE. (It is thought that cows acquired the infectious prions by eating feed made from sick animals, a theory that doesn't apply to deer and elk, who are still mostly grazers.) A recent study conducted by the Wildlife Research Center in Colorado found that CWD is passed with relative ease among deer kept together in a penned environment—within four years, 90 percent of the experimental group contracted the disease simply by living together. Scientists are still unsure about what transmits the pathogen: The evidence suggests that the disease must somehow linger in a shared grazing environment—likely in feces, urine, or saliva. The epidemic seems to have been exacerbated, then, by the close proximity of deer and elk on game farms and wildlife research facilities, and/or in areas where people bait and feed wild animals for hunting.

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It's difficult to determine the size of the epidemic. Wild populations are hard to survey, and in any case there is no practical way to test for the disease in live animals; state wildlife departments base their estimates of infected animals on tests of found animal carcasses, animal heads voluntarily submitted by hunters, and, in some states, deer taken down by state sharpshooters. In the affected areas, the percentage of sick animals can range from less than 1 percent to 15 percent of the wild deer population and less than 1 percent of the wild elk population. (In destroyed captive herds, though, disease rates have been as high as 70 percent.) Some states—Colorado and Wisconsin, for example—are acting on the theory that the disease will not reach its own equilibrium and are thinning herds in order to prevent the spread of the disease. Deer and elk ranchers have been devastated by the disease: A single positive test on a ranch can mean quarantine for the animals and possible liquidation of a rancher's herds. In defense, ranchers have responded with more aggressive testing measures to prove the health of their herds.

The good news about CWD is that—at least so far—there is no established link between eating or handling venison and vCJD, the devastating human disease linked to beef consumption in England. And, though research at this moment is not yet complete, CWD has not seemed to infect the unlucky cows, goats, and sheep that have been kept in close quarters with infected deer and elk. Still, TSE diseases develop slowly, over a minimum of 15 months to 17 months after exposure, and there is not yet enough evidence to rule out cross-species transmission altogether. Having learned from the British government's mistakes in the BSE crisis, no national or state government agencies have made out-and-out exhortations to continue eating venison from the infected areas (e.g., à la John Gummer, the British secretary of agriculture who famously endeavored to demonstrate the safety of British beef by feeding a hamburger to his 4-year-old daughter). But the issue is complicated by the fact that those who consume venison and elk meat are often the hunters who slaughter the animals—they thus must decide for themselves whether their quarry is safe for consumption. (Beef, by contrast, is inspected at the slaughter and packing levels—or is supposed to be—before consumers eat it.) Plus, hunters who butcher their own game are at higher risk of being exposed to the neural and lymph node tissue that carry far more prions than a venison steak from the muscle tissue of the deer. (Though, again, so far no one has gotten sick from eating or handling deer from CWD-affected areas.)

How did the CWD epidemic come about? The disease was identified in a Colorado research farm in 1967 and recognized as a TSE in 1978. For a long time, it seemed to be confined to wild and farmed populations in the area where Colorado, Wyoming, and Nebraska intersect. But since 1997, the disease has spread to at least 12 states and two Canadian provinces. In 2002, when infected deer were discovered east of the Mississippi, in Wisconsin, the disease suddenly seemed much more pervasive. This geographic leap was likely spurred by the interstate traffic of live deer and elk to stock game farms, which increased in the '90s as a result of the high demand for game meat on upscale menus, as well as for antler velvet, which is valued as a potent regenerative treatment in Asian herbal markets. In some states, too, transmission was likely encouraged by "canned hunts," where fences and a high concentration of animals ensure a shooter's success. These days, more and more states are banning the importation of live deer and elk, as one Michigan couple learned when they were held by police for hauling a trailer full of "pet" elk and deer they had purchased in Ohio. And the days of strapping a carcass across the hood of the car are surely numbered, as many states have begun to insist that only boned-out, butchered meat be taken across state borders.

Late last year, Congress increased dollars for CWD research and prevention to $4.2 million, $1 million more than the year before (and compared to $13 million budgeted to BSE this year, before the president's post-mad cow discovery request of $60 million for 2005). Affected states now find themselves in the awkward position of trying to promote hunting in the face of a mysterious and unsettling disease. Hunting, after all, has for decades now been the method states use to regulate the deer population (and, according to the U.S. Fish and Wildlife Service, a source of tens of billions of dollars of national revenue from equipment, travel, and lodging expenditures). For the moment, controlling the disease involves continued surveillance; making sure sick animals aren't moved from region to region; enlisting hunters to voluntarily submit deer heads for study and tracking; and in some states, like Colorado and Wisconsin, slaughtering animals—both healthy and sick—in areas where infected deer are found. Wisconsin has even begun offering bounties to hunters who submit deer heads that turn out to be positive to state testing facilities.

What about those of us who don't hunt, but occasionally prepare or consume venison? As a professional cook, I've often chosen offbeat meat like venison in favor of beef or chicken. Rational or not, I liked the feeling that my deer, boar, bunny, or pigeon didn't come from the kind of industrial feedlot implicated in the spread of salmonella and BSE. But the stubborn presence of CWD has made me question my instincts about more "natural meats." Until I know more, venison from New Zealand (where every animal is tested and there's not been a single case of the disease) seems more appealing—and possibly safer—than home-grown.

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