Chronic Wasting Disease

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Over the past 20 years, chronic wasting disease (CWD) in Wyoming has been spreading slowly outward from the southeastern corner of the state toward the Greater Yellowstone Area and Wyoming's elk feed grounds, where more than 24,000 elk are supplementally fed each winter.

 

Recently, the disease was detected in mule deer and elk around the supplemental feeding grounds and Grand Teton National Park-- setting off renewed concern about the impact of CWD in the Greater Yellowstone Ecosystem (GYE). These feed grounds facilitate dense aggregations of elk during the feeding season, and it is these high elk densities that may put feed ground elk at greater risk of CWD spread and subsequent declines in survival and population growth. Studies show that CWD prevalence tends to be higher in mule deer than elk and Wyoming surveillance data suggest that CWD in mule deer is more widely distributed across the state.

 

Salt lick (right) and device to exclude wildlife from access to minerals (left)

Orange and black excluder device (left) will contain minerals, but intended to allow livestock access while excluding wildlife. Mineral block to the right of excluder device.( Credit: Paul Cross, USGS. Public domain.)

Current Projects

1. Assessing the role of artificial mineral licks in CWD dynamics (for CWD-mineral licks website, click here)

Management strategies to control and slow the spread of CWD into non-endemic areas rely in part on limiting higher prevalence “hotspots” which may center around limited resources that increase wildlife host densities. Agricultural mineral tubs and salt licks have been observed to be visited by deer and other cervids and may serve as a fomite for CWD transmission. This can occur by animals successively visiting and licking a tub or block or licking the salt that leaches into the ground around these sites. Elemental additives to salt such as copper and manganese may have the added effect of increasing the longevity and transmission potential of CWD prions (Nichols et al, 2016). Our goal is to determine how important anthropogenic mineral licks are to the transmission of CWD.

Contacts: Paul Cross, USGS; Brant Schumaker & Bevin McCormick, University of Wyoming

 

2. Effects of cougar predation on CWD dynamics in Wyoming mule deer

Mountain lions in Montana

Mountain lions prey on ungulates like mule deer and it's hypothesized that they may selectively remove infected prey. (Credit: USGS, Public domain.)

Predators have been hypothesized as a potential disease sanitizing agent by selectively removing infected prey. This idea has been developed theoretically and has been demonstrated in other field systems. For CWD, however, there is only one modeling study of the potential effects of predation and one study of cougar predation on mule deer. Several questions remain, and replication in other regions is needed.

We hope to understand if predation by mountain lions is related to overall population prevalence of CWD in mule deer, and if predation of infected deer is disproportionate to availability.

Primary Contacts: Joe Holbrook, University of Wyoming; Kevin Montieth, USGS Wyoming Cooperative Fish and Wildlife Research Unit; Justin Binfet and Justin Clapp, WGFD; Paul Cross, USGS.

 

3. Estimating the effects of artificial feeding at the National Elk Refuge on elk contact rates

Elk in Wyoming

Elk captured using a camera trap. Elk are susceptible to chronic wasting disease. (USGS, Public domain.)

In November 2018 chronic wasting disease (CWD) was detected for the first time in Teton County, Wyoming, in the heart of the globally-significant Greater Yellowstone Ecosystem (GYE). The detection occurred in a mule deer in Grand Teton National Park (GRTE) near the northern boundary of the National Elk Refuge (NER). Elk that winter on the NER are managed under the USFWS Bison and Elk Management Plan, in collaboration with the Wyoming Game & Fish Department (WYGFD). NER elk densities greatly exceed levels predicted to result in rapid population declines with the introduction of CWD. NER management options that influence animal aggregation and distribution include feeding and hunting.  We are quantifying elk contact patterns on the NER and the role of supplemental feeding in modifying potential CWD transmission. We are also developing methods to more cost-effectively estimate elk densities using tools including satellite imagery and unmanned aerial systems and to evaluate the success of adaptive management in changing densities and degree of concentrations of elk. For more information on developing tools to evaluate chronic wasting disease transmission risk, click here.

Primary Contacts: Tabitha Graves, USGS; Eric Cole, USFWS; Will Janousek, USGS

 

4. Modeling the role of predation in CWD dynamics

The combined effects of wolves and cougars on CWD in the Rocky Mountain West will not be empirically estimable for decades given that CWD is slow to develop, and only recently did the CWD distribution begin to overlap with areas containing suites of predators. Additionally, managers lack timely indicators of CWD presence in host populations. We currently rely on the non-invasive sampling of wolf-killed, cougar-killed, and road-killed cervids, as well as harvested elk and deer to monitor for CWD in Yellowstone and Grand Teton National Parks and Wyoming. This method of collection produces small sample sizes and needs to be supplemented with wider geographic sampling and alternative approaches. We propose to simulate the potential role of different predators and identify key indicators of CWD invasion in elk and deer in the Greater Yellowstone.

Contacts: Paul Cross, USGS; Nathan Galloway, NPS; Ellen Brandell, Penn State University

 

5. Modeling alternative hunting strategies on CWD, deer and elk dynamics

Male deer and elk are often found to have higher prevalence of CWD than females.  There are multiple mechanisms that may drive this observed pattern. Female to transmission to males may be high due to male mating behaviors. In this case, males are being exposed at higher rates resulting in higher prevalence, but are not necessarily the most responsible for transmission.  This has potential management implications for the efficacy of male-biased harvest. In this project we explore the consequences of different harvest management regimes under different transmission scenarios between male and female deer using age-structured disease models.

Contacts: Paul Cross, USGS; Will Rogers, Montana State University

 

6. Maternal effects and chronic wasting disease in Wyoming mule deer

Previous CWD work tends to focus on adult survival and reproduction. We are interested in intergenerational effects of CWD. So, we are following mothers of known CWD status as well as their fawns to understand multiple maternal effects.  How does a mother’s CWD status affect fawn condition and survival? How do dispersal rates and distances of fawns differ depending on the CWD status of the mother? How much more likely are fawns of CWD positive mothers to become CWD positive?

Primary Contacts: Kevin Montieth, USGS Wy. Coop Unit; Rhiannon Jokopak, University of Wyoming; Joe Holbrook, University of Wyoming; Justin Binfet, WGFD; Paul Cross, USGS.

 

Past work:

Our past work on CWD focused on modeling efforts to understand how a persistent environmental reservoir may affect long-term disease dynamics and population dynamics of deer and elk. In addition, we worked on assessing mule deer connectivity around Montana by contributing to collaring efforts as well as using genetic methods.

 

Mule deer in Wyoming with snow covered mountains in the distance

Mule deer are susceptible to chronic wasting disease. (Public domain.)