Down deer, ill elk

Cow Madness

About 4 to 6 percent of mule deer in parts of Colorado and Wyoming have chronic wasting disease, a relative of mad cow.
© Wes Nowotarski

Rocky Mountain mauler
Chronic wasting disease spreads through deer and elk by a different route than mad cow. Amidst all the furor over BSE in Europe, a similar illness among deer and elk gets much less fanfare. (Want The Why Files guide to mad cow lingo?)

The TSE in question is called chronic wasting disease, and it's been found for decades in two western states. Less than 1 percent of Rocky Mountain elk, and 4 percent to 6 percent of mule deer and white-tailed deer in southeast Wyoming and northeast and north-central Colorado have chronic wasting disease, says Elizabeth Williams, a professor of veterinary science at the University of Wyoming and a pathologist at the state veterinary laboratory. The disease is also present in captive herds in five or six states, she adds.

Williams, who has studied the problem for two decades, says the numbers has been very stable, especially for the past four years in Wyoming, where a large sample produces solid statistics. "It's a slow, chronic disease, and we wouldn't expect wild swings of prevalence."

The disease is diagnosed from slides of brain and lymph tissue made with sensitive immune techniques, she says. In fact, the detections are so sensitive that the "percentages of affected animals we find are not readily comparable to data on other spongiform encephalopathies," she says. Tests of tonsils may detect disease just 42 days after inoculation, extremely early for a TSE.

Vulnerable vegetarians
Gray bodied, with tawny antlers, white face and black eyes and nose, the deer looks directly at the camera. Mad cow spreads when cows eat remnants of other cows. Deer and elk are vegetarians -- hardly what you'd call cannibals. How do they get wasting disease?

Williams says the TSE could move either from mother to offspring, or horizontally from one animal to another. "Given the amount of disease in the area, and to fit the epidemiology, it has to be transmitted horizontally."

She says the probable mechanism is fecal-oral transmission. "Somehow the agent gets into the feces, and an animal comes along and consumes forage" contaminated with feces. Alternatively, the prion could be present in saliva. An upcoming research project will address transmission issues.

Hunting for trouble
The wasting disease outbreak seems ripe for a "jump" to humans -- either directly to hunters or through cattle. Colorado and Wyoming both recommend that hunters limit their exposure to spinal cords and brains by using rubber gloves while cleaning kills.

Standing in a field of brown grass, the brown elk gazes at the camera, with a huge rack of antlers held aloft. The tail is whitish, and the face black. Less than 1 percent of elk in parts of Colorado and Wyoming have a TSE.
Courtesy U.S. Fish and Wildlife

But Williams does not evince a huge level of concern. "The main thing is that people are informed, you decide where to hunt, nobody makes you hunt in a place with high prevalence." Williams says while she does recommend rubber gloves, she does not follow the rule when she hunts.

Nobody is known to have been sickened directly by chronic wasting disease, and there is no evidence that cattle have been infected. However, as biologist Tom Pringle points out, these is some evidence that this prion could infect people more or less as readily as the BSE prion does.

Translated: Chronic wasting disease could be as dangerous as mad cow.

What's being done to protect the U.S. food supply?

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