CHRONIC WASTING DISEASE
Kip Adams, QDMA Director of Education and Outreach, Northern Region
In fact, unless you were from Colorado, Wyoming or a handful of other western states, you probably hadn’t
heard of CWD or at least didn’t know much about it. Today, the picture is much different. You would be hard
pressed to find a deer or elk hunter anywhere in North America who hasn’t heard of CWD. Unfortunately, we
know surprisingly little about the disease, although scientists have recently uncovered some new facts. This
article will cover some of those discoveries and discuss CWD’s impacts on the future of deer hunting.
In 2002 CWD was confirmed in Wisconsin from three bucks killed near Mount Horeb in November 2001. This
marked the first incidence of CWD east of the Mississippi River. This was a major discovery because the
disease was now in a high-density deer population. Many western deer herds average less than 15 deer per
square mile while Wisconsin has herds exceeding 45 deer per square mile. This was important because infected
deer can pass the disease to other individuals, and high density herds, especially those in close proximity
such as at feed sites, provide an avenue for high disease transmission rates. Scientists knew deer could pass
the disease to other deer but were, and still largely remain, unsure of exactly how they do it.
As of December 2006, CWD has been identified in captive and free-ranging herds in 14 U.S. states, 2 Canadian
provinces and Korea (from an elk imported from Canada in 1997). CWD has been identified in white-tailed
and mule deer, Rocky Mountain elk and moose. Black-tailed deer are also susceptible as they are a subspecies
of mule deer. Much research has been conducted on CWD and much continues today, but we still don’t
know the origin of the CWD agent(s) in cervids (deer, elk and moose) and likely never will.
Fortunately, research suggests the disease won’t cross the species barrier and infect humans. The World
Health Organization and Center for Disease Control both state there is no evidence that humans can contract
the disease from eating CWD-infected cervids. This statement is important as the infective prions (abnormal
forms of cellular protein) causing CWD accumulate in an animal’s brain, eyes, spinal column, tonsils, lymph
glands, spleen, saliva, blood and muscles. The last two locations are most noteworthy for humans since we
come in contact with blood while field dressing and/or processing a harvested animal and we eat the muscle
tissue. Research suggests prion concentrations may be somewhat lower in muscles than other tissues but
they are still present.
A new study recently identified the prions in blood and saliva. These locations are important from a disease
transmission standpoint. It raises the possibility that biting insects that feed on blood may have the ability to
transfer the disease from CWD-positive animals to other individuals. It also raises the possibility that CWDpositive
animals can transmit the disease via saliva at bait stations, feed and mineral sites, rubs, scrapes and
through social grooming. We all know the branch above a scrape is referred to as the “licking” branch and we
know bucks lick and rub their forehead glands on rubs. Many hunters have also viewed submissive bucks licking
a dominant buck’s forehead. Young bucks, especially yearlings, are generally submissive to older bucks.
We know a high percentage of yearling bucks disperse one to five miles from their natal range, so infected
yearling bucks potentially could serve as major disease transmission vehicles. I say they “potentially could
serve” because I am merely speculating. Research hasn’t identified this occurring in free-ranging populations.
Also, the disease doesn’t appear to move within a region by leaps that would result from yearling dispersal.
Future research will hopefully shed more light on exact modes of transmission.
What do we know about CWD? We know it is always fatal and there is no vaccine, cure or practical live animal
test. The best current live animal test uses tonsil tissue but it is ineffective in elk and not applicable for large
scale use in deer. We know the probability of infection increases with age in whitetail bucks and does and that
adult bucks are nearly twice as likely as adult does to be infected. You need to keep this statistic in perspective
however, as many deer populations contain a much higher percentage of adult does than bucks. This finding
isn’t a reason to return to traditional management programs and remove the majority of bucks at an early age.
We know the clinical signs of CWD are emaciation, incoordination, a drooping head and ears, and excessive
drooling, drinking and urination. It is important to note these symptoms are also seen in deer infected with EHD
or bluetongue. EHD and bluetongue are the most common deer diseases and they routinely kill deer throughout
the Southeast on a nearly annual basis. We know CWD’s clinical signs typically develop from one and a
half to three years after exposure. Thus, infected deer generally appear healthy while they may be passing the
disease to others. No deer has ever recovered once clinical signs developed and animals generally live from a
few weeks to several months after developing clinical signs. We also know that CWD can be expensive. Wisconsin
has spent over $32 million on CWD from 2002-2006, and sadly the CWD infection rate in the “core area”
of Wisconsin hasn’t declined.
As hunters and managers, what can we expect in the future? We can expect CWD will likely be found in
new states/provinces and new areas in current CWD-positive states/provinces. We can expect to see a lot of
research on CWD, its mode(s) of transmission, etc., and we can expect pressure from deer farmers to open
state/provincial borders and allow movement of captive animals. We can also expect changes in deer season
regulations such as extended seasons and increased bag limits. Currently, the best way to limit the spread of
CWD in free-ranging herds is to reduce deer populations to minimize contact between individuals.
Will CWD mark the end of deer hunting? Probably not, but we must be vigilant to balance deer herds with
their habitats, minimize transmission of CWD in infected areas, prevent introduction of CWD in new areas, and
support research and our state agency’s efforts. The sum of these items equates to being a good steward of
our deer resource. For more information on CWD visit the Chronic Wasting Disease Alliance website at www.
Kip’s Korner is written by Kip
Adams, a Certified Wildlife Biologist and Northern Director
of Education and Outreach for the Quality Deer Management
Association (QDMA). The QDMA is an international nonprofit
wildlife conservation organization dedicated to ethical
hunting, sound deer management and preservation of the
deer-hunting heritage. The QDMA can be reached at
1-800-209-DEER or www.QDMA.com.