Essential Facts on Chronic Wasting Disease

By  Will Hueston, DVM, Ph.D.

Chronic wasting disease is a slow-onset, brain-degeneration disease that affects deer and elk. Scientists have known about it since 1967, but it was long considered an anomaly, and has only caught the popular media's attention in the past few years, as it has begun to spread. Most people hadn't heard about it until the media reported on a case in Wisconsin in spring 2002.

Chronic wasting disease was first found in research facilities in Colorado and Wyoming. Then in the 1980s and early 1990s, it was found in wild elk, mule deer, and white-tail deer in the same area. In the last few years, through the movement of breeding stock, it has been spread in the farmed-elk population across the country. And most recently, chronic wasting disease has been identified in free-roaming deer in a number of states, including Nebraska, South Dakota, Wisconsin, Illinois and New Mexico.

It's a disease associated with a brain protein called a prion. Such proteins are shared by all mammals, including humans. With the onset of a prion disease, these proteins change shape and, essentially, the abnormally shaped proteins pile up and damage the brain. Chronic wasting is member of a group of diseases that includes: scrapie, a sheep disease; BSE, or "mad cow" disease, which affects cattle; and some rare human diseases, like Creutzfeldt-Jakob disease. Thankfully, most of these diseases appear unique, with no relationship to each other. The prion diseases that affect humans are very rare: the most common one is the spontaneous form of Creutzfeldt-Jakob, which occurs at a rate of roughly 1 in 1 million people per year. Those cases are distributed globally, regardless of diet, background, or environment.

In deer and elk, chronic wasting disease is probably spread through direct contact, either nose to nose or through saliva or other bodily secretions. Can it be transmitted to people? Well, let's look at the potential for human exposure and our knowledge of this group of diseases. There exists the possibility people could be exposed to the disease through direct contact with a wild animal, but few of us have nose-to-nose interactions with wild deer or elk.

Hunters, of course, might come in contact with a deer or elk with CWD. Public Health experts recommend good common sense-avoid contact with animals whose ribs are showing, whose ears are drooping, or which just don't look healthy. We recommend that hunters leave such animals alone (for example, do not shoot them) and report the sighting to the state agency overseeing hunting, so that the agency can collect the animal and test it.

And what about eating venison? In recent months, there have been news reports about a handful of individuals suspected to have prion diseases. The media has noted that some of these individuals enjoyed hunting or eating venison and, not surprisingly, that has raised questions about the possible transmission of chronic wasting disease to humans. Those are important questions to ask. Investigations to date, however, have found no convincing evidence of a connection between the human prion disease and chronic wasting either in monitoring the potential for natural exposure or in laboratory experiments.

Still, individuals who consume venison might wisely try to reduce their potential exposure to the disease. Here's the good news: Researchers studying natural prion diseases like CWD have never found them in muscle meat. They manifest themselves in the brain, spinal cord, lymph nodes, and spleen. So if you're aware of the scientific evidence but still interested in minimizing your potential for exposure, you can do so by avoiding any of those animal parts. Those are the prudent, practical, and pragmatic risk-management strategies that one can take.