What About Mad Deer Disease?

Although the USDA is quick to proclaim that mad cow disease has never been detected in the United States, it is less eager to talk about a similar disease that is occurring here—chronic wasting disease (CWD), a transmissible spongiform encephalopathy that is similar to mad cow disease except that it occurs in deer and elk instead of cattle.CWD was first discovered in the 1960s and has since been spreading slowly through the deer and elk population, mostly in a few western states such as Colorado and Wyoming. A few cases have also been detected in Canada. Mike Miller of the Colorado Division of Wildlife describes CWD as "an epidemic occurring in slow motion."

Illustration by Todd M. Coe

In recent years, two hunters and a woman who regularly ate venison have died from Creutzfeldt-Jakob Disease (CJD) in the United States. Dr. Ermias Belay of the U.S. Centers for Disease Control and Prevention has studied the circumstances related to the three deaths. They’ve raised concern, he notes, primarily because of the unusually young age of those infected. Like mad cow disease and CWD, CJD is a transmissible spongiform encephalopathy that kills its victims by filling their brains with microscopic sponge-like holes. It occurs throughout the world but is quite rare, accounting for an estimated one death per million people per year. Moreover, CJD almost always occurs in people older than age 45, yet all three of the venison-eating victims in the United States contracted their disease before the age of 30.

In a January presentation to the Food and Drug Administration, Belay noted that the unusually young age of the victims, combined with the fact that they all ate venison, suggested "a possible relationship with CJD." His review of the evidence found no common genetic or clinical signs that would point to CWD as the cause, and therefore he concluded that there was "no strong evidence of a causal link." However, absence of proof is not proof of absence. He added, "Our conclusions are limited to three patients, and continued surveillance remains very critical to continue to monitor the possible transmission of chronic wasting disease to humans."

The three victims" brains were autopsied by Dr. Pierluigi Gambetti, professor of pathology and director of the National Prion Disease Pathology Surveillance Center at Case Western University in Cleveland, Ohio. Like Belay, Gambetti did not find proof that the hunters died from exposure to CWD, but he did not find anything to disprove it either.

Gambetti says that he personally will avoid eating venison. "Why should I? I can eat something else," he says. "But that’s not because I really think there is great danger. I just think the whole issue of prion disease in the United States, both in animals and humans, has to be confronted seriously. We really have to do more." Gambetti is hesitant to say there is danger of an epidemic, but he agrees that more research is needed.

"The deer issue is potentially a problem," CJD expert Paul Brown of the National Institutes of Health said recently at a meeting of CJD Voice, a support group for family members of CJD victims. "I don’t think it’s a problem yet, but I think it could possibly explode," Brown said. "What we’re seeing in this country is a handful of cases that has excited the popular imagination because of the possible association with deer and venison and elk [and] the geographical association. A cause-and-effect might be established, in which case it will be very important. Or it might be a chance cluster of a few young people due to random clumping alone, and when we look at it in five years, we may not see any more."

But while scientists continue to study the question, without any clear evidence one way or the other, hunters in the U.S. continue to eat venison from animals with a disease that definitely kills the animals themselves and may turn out to kill human beings.