What’s in a name? Chronic wasting disease sounds ominous, too descriptive for comfort, almost impolite in its directness. It is, in fact, a truthful name for a disease and a real threat to North America’s cervids.
Chronic Wasting Disease
Can Science Save Our Dear Deer?
Cervids encompass animals in the deer family, including white-tailed deer, mule deer, reindeer, elk and moose. CWD is an always-fatal wildlife disease that is contagious among free-ranging and captive cervids. Its neurological impacts result in brain damage that causes affected animals to slowly waste away to death. CWD is spreading and has been detected in more than half of U.S. states as well as in Canada, South Korea, Norway, Finland and Sweden. Currently, there’s no treatment or vaccine.
“Big game like deer and elk are valued by people for food, and they’re culturally important to tribal communities and hunters in North America,” said Bryan Richards, emerging disease coordinator at the USGS National Wildlife Health Center. “Cervids are also intrinsically valuable. That’s why we care about this disease.”
Richards and many other USGS scientists across the U.S. are working to understand the biology of CWD, assess and predict the spread of the disease and develop tools for early detection and control.
CWD is not known to directly affect humans or livestock, but it plagues people nonetheless. Cervids are fundamental to America’s outdoor recreation economy (PDF), which generates billions of dollars in consumer spending annually and billions more in federal, state and local tax revenue, according to the Outdoor Industry Association. The U.S. Fish and Wildlife Service found that wildlife-related recreationalists spent $156.9 billion on their hunting, wildlife watching/photographing and angling activities in 2016. Big game, including deer and elk, was the most common type of hunting.
“Healthy environments bolster healthy economies,” Richards said. “Unhealthy animal populations do the opposite.”
For these reasons, CWD is of great concern to wildlife managers, but managers need information to make key conservation decisions. That’s where USGS science comes in.
The Scoop on the Scope
Adult male cervids are the most vulnerable to CWD. More than 40% of free-ranging cervids in this category are infected with CWD in the heavily affected areas of Colorado, Wisconsin and Wyoming. As of July 2020, CWD was detected in 26 U.S. states and three Canadian provinces, a sobering statistic that includes free-ranging cervids and/or commercial captive cervid facilities.
“The CWD problem is significant and the disease is growing and spreading,” Richards said.
True to USGS's map-making legacy, the bureau maintains a map to track the spread of CWD. The USGS Expanding Distribution of Chronic Wasting Disease map for North America is used by federal, state and academic partners to understand where the disease exists and where it moves on the landscape. The map uses data from state wildlife agencies, the U.S. Department of Agriculture and the Canadian Food Inspection Agency, and it’s been updated regularly since 2005.
The CWD spread map can be used in conjunction with products that document big-game migration corridors, such as new maps developed by the USGS and partners to track over 40 big-game migration routes. Facilitated by Department of the Interior Secretary’s Order 3362, these new maps will help land managers and conservationists pinpoint actions necessary to keep migration routes open and functional to sustain healthy big-game populations.
A Simulation Tool to Assist CWD Management
Hunters play a role in wildlife management, and altering how deer, elk or moose are harvested is one of the primary ways that CWD can be managed. With this in mind, the USGS, in collaboration with Montana Fish, Wildlife and Parks, developed a tool to simulate different scenarios associated with CWD over a 5- to 10-year time horizon based on a set of assumptions about how the disease spreads.
The CWD simulation app allows decision-makers to enter parameters for deer or elk populations, hunting mortality and disease transmission. Users can run scenarios for a species and region of interest by modifying parameters. The model provides the estimated number of deaths, along with age and sex distribution, and how many were natural, hunting or CWD-related. These results can provide resource managers with critical information to help slow the spread of CWD.
“This tool provides an easy way for natural resource managers to think through the potential effects of different harvesting strategies and how long it may take to observe any changes,” said Paul Cross, a scientist at the USGS Northern Rocky Mountain Science Center. “We are also developing inexpensive ways to measure cervid density and identifying high concentration areas to help facilitate adaptive management to reduce disease risk.”
Cross and other scientists at the science center have several research projects dedicated to understanding CWD.
CWD in Your Parks
Even if you’re an urbanite, or you don’t live on or near property that’s commonly visited by cervids, CWD is on your land – our national parks – and so is the USGS.
“National parks belong to the public, and the USGS is supporting the National Park Service in their efforts to manage CWD within park boundaries,” said Glen Sargeant, a scientist with the USGS Northern Prairie Wildlife Research Center.
For example, past USGS research found that CWD was the leading cause of death in Wind Cave National Park’s elk population. Now, USGS scientists are studying the relationship between elk population density and CWD prevalence and evaluating the effectiveness of the park’s elk population-control efforts in curtailing disease spread. Findings can help guide CWD-related management decisions in other parks and preserves with high-density elk populations.
Further work by USGS scientists and partners in Shenandoah National Park may help improve early detection of CWD. Traditionally, scientists and managers have monitored the disease in deer by collecting samples randomly and broadly. In a 2018 study, scientists developed and used a computer simulation to hone in on white-tailed deer in Shenandoah that have a higher risk of disease, such as older males.
“With this new approach, researchers can test fewer numbers of deer by using existing information on the disease risk of different demographic groups,” said Daniel Walsh, a USGS scientist and coauthor of the study.
Surveying animals with the greatest likelihood of sickness rather than the entire population can save time and money and allow for a quicker response if CWD is detected.
Prions: Gross or Engrossing?
CWD is caused by prions, which are misfolded, abnormally-shaped proteins in the body. Mammals regularly produce healthy proteins that are broken down by cells, but prions associated with disease accumulate in parts of the body such as the brain and spread by infecting the normal proteins. Mad cow disease and scrapie are prion diseases, but CWD is the only such disease known to affect free-ranging wildlife.
Prions and Early Disease Detection
Currently, CWD is typically detected once an affected animal has died by looking for prions in the animal’s tissue. However, USGS scientists are working to expand the options for CWD testing to gain a more thorough understanding of the disease.
“The USGS is enthusiastic about efforts to develop advanced, state-of-the-art CWD-testing techniques that go beyond carcass tissue sampling,” said Cynthia Tam, Invasive and Disease Program Coordinator for the USGS Ecosystems Mission Area. “These tests will look for prions in biological samples from live animals and in samples taken from the environment.”
For example, scientists hope to collect prions from biological samples such as fecal material and blood, and from environmental samples such as soil. The ability to test for CWD using these samples from live animals and from the environment will greatly enhance critical surveillance and early detection of the disease.
Old Data, New Science
Managers have long used animal harvesting or hunting policies to slow the spread of CWD. Agencies often adjust hunting regulations in CWD-affected areas to help reduce cervid population density and curtail animal-to-animal infections once CWD is detected. However, the effectiveness of this strategy in slowing CWD has been difficult to measure.
A new scientific project led by the USGS Wisconsin Cooperative Wildlife Research Unit will examine past animal harvest strategies and policy actions to help determine how they may be used to affect CWD going forward. Results will help inform adaptive management techniques, including disease management and monitoring over time.
“The USGS Wisconsin Cooperative Wildlife Research Unit is an essential partner in linking research with real-world wildlife management,” said Mark Rickebach, chair of the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison. “Whether maintaining habitat for songbirds or addressing the vexing problem of CWD, the unit leverages expertise from across campus to bring the best science to bear.
The unit’s emphasis on graduate training ensures that future scientists and leaders understand the connection between science and management, Rickebach added.
Providing management with the best science possible is, after all, the USGS mission. It’s also the most effective strategy for controlling North America’s most complicated – and chronic – wildlife disease.
As CWD progresses, so will USGS research to combat its spread. In October 2020, the America's Conservation Enhancement Act (PDF) became law, calling for an official CWD task force. Section 104 of this new law authorizes $5 million for the U.S. Fish and Wildlife Service, a fellow DOI bureau, to execute an interstate action plan for CWD and $1.2 million for the USGS to carry out a CWD Academia Resource Study on the disease’s spread. The USGS study will provide science-based recommendations to help minimize the risk of CWD transmission within or between cervid herds.
If you see sick or dead wildlife, please contact your state department of natural resources or state game and fish agency.
The information provided in this story is a sampling of the CWD research being conducted by the USGS and its partners. To explore the larger scope of CWD science across North America, please browse through the following resources.
USGS Quick Links
- USGS Outstanding in the Field podcast: Episode 3, Chronic Wasting Disease
- USGS Story Map on CWD
- Fact Sheet: U.S. Geological Survey Response to Chronic Wasting Disease
- Map: Distribution of Chronic Wasting Disease in North America
- USGS Chronic Wasting Disease Simulation App
- USGS National Wildlife Health Center
- USGS Northern Rocky Mountain Science Center
- USGS Northern Prairie Wildlife Research Center
- Wisconsin Cooperative Wildlife Research Unit
- Pennsylvania Cooperative Fish and Wildlife Research Unit
- Centers for Disease Control and Prevention’s CWD website
- U.S. Department of Agriculture – Animal and Plant Health Inspection Service CWD website
- Great Lakes Indian Fish & Wildlife Commission – CWD page
- Wyoming Migration Initiative
- Weighted Surveillance for Detection of Chronic Wasting Disease application