AgBioResearch

The common slang term for a one-dollar bill — buck — is actually a direct reference to the importance of deer hide, or buckskin, as a unit of trade in the 18th century. Today, while more of a pastime than livelihood, hunting — and deer hunting in particular — retains a major cultural and economic impact.

More than 13 million American hunters generate more than $33 billion in economic impact, according to the National Survey of Fishing, Hunting and Wildlife-Associated Recreation. Michigan has nearly 800,000 licensed hunters, 90 percent of whom pursue whitetailed deer. They generate some $2 billion in economic impact, ranking Michigan third in the nation. Recently, however, there is a new threat to the Michigan deer population — chronic wasting disease (CWD).

In May 2015, a six-year-old whitetailed deer in Ingham County was identified as being afflicted with CWD, the first confirmed case in the state in a wild deer. Since then, the Michigan Department of Natural Resources (MDNR) has tested nearly 12,000 wild deer and documented nine other cases in Ingham and neighboring Clinton counties.

Two additional cases have been reported this year on a Mecosta County deer farm. To help formulate a plan to control further CWD outbreaks and prevent the disease from gaining a foothold in the state, Michigan State University (MSU) wildlife researchers William Porter and David Williams are bringing expertise in deer behavior and population dynamics to identify where new cases are most likely to appear.

“In broad terms, the question is: can we stem the emergence of chronic wasting disease in Michigan?” said Porter, the Boone and Crockett Chair of Wildlife Conservation in the MSU Department of Fisheries and Wildlife. “We need to detect it when it’s still rare so that we can manage the deer population to keep it under control and, perhaps, eliminate it.”

A disease of the nervous system exclusive to members of the cervid family — deer, elk, moose, caribou and other hoofed, antlered, ruminant mammals — CWD is similar to mad cow disease. Caused by a malformed protein piece called a prion, CWD builds up in brain and spinal tissue, where it begins to self-replicate and causes widespread neurological degeneration. The fatal disease manifests in a range of behavioral issues, including listlessness, tremors, nervousness and increased thirst, as well as weight loss over time.

There is no known cure or vaccine for CWD. First identified in the United States in 2002, CWD is notoriously difficult to control. The disease spreads through direct fluid contact and the infectious protein agent is shed into the environment, where it can persist for over a decade.

“As nonliving pathogens, these prions are extraordinarily resilient to efforts to destroy them. You can’t incinerate it, you can’t treat it successfully with chemicals, there’s no known way to cleanse a contaminated environment,” Porter said. “You can’t kill it because it’s not alive.”

All is not lost, however. Porter and Williams first crossed paths with CWD when it was discovered in 2005 in New York and helped to prevent it from becoming endemic. Williams was conducting research for his doctoral dissertation at the time, studying how to apply knowledge of deer behavior and interactions to predict where CWD was most likely to appear in the landscape.

Working with Porter and the New York Department of Environmental Conservation, the scientists produced a model that combined information on deer movement, habitat use and interactions that marked regions of high CWD likelihood. New York’s wildlife managers used this model to develop an intensive deer culling strategy, and by 2010, no new cases of CWD were being reported. Porter and Williams are attempting to adapt this same approach in Michigan.

The first step in developing a predictive model is identifying the CWD transmission risk factors. Priority regions are identified on the basis of dense deer populations, proximity to bordering states such as Wisconsin, where CWD is already a significant problem, and large numbers of out-ofstate hunters who may inadvertently transport CWD into the state. They also aim to use disease transmission models to map how and where CWD might spread from those first priority regions.

The danger that CWD poses to Michigan’s deer population and its hunting and conservation endeavors cannot be understated. Revenue generated by deer hunting is used by the MDNR to fund a wide range of conservation efforts throughout the state, including efforts to rehabilitate populations of Kirtland’s warbler and sandhill cranes.

“CWD represents a threat to the very fundamentals of all fish and wildlife conservation,” Porter said. “Deer in Michigan are iconic, like beaches are to Florida — they’re part of the fabric of who we are. We are looking at a disease that has the potential to drive a stake into the heart of all conservation in the state, and we want to deliver to the MDNR a means to identify high-risk areas so we can stop CWD before that happens.”