USGS Chronic Wasting Disease Research at NOROCK Active

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.

Current and Recent Projects

Assessing the role of artificial mineral licks in CWD dynamics

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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.

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

Predation and CWD

Effects of cougar predation on CWD dynamics in Wyoming mule deer

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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.

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

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

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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.

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

Evaluating management alternatives to supplemental winter feeding of elk: A structured decision-making approach

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Elk are provided supplemental winter feed at twenty-two sites in the southern region of the Greater Yellowstone Ecosystem in Wyoming. One of those sites is the National Elk Refuge, managed by the U.S. Fish and Wildlife Service (USFWS) while the rest of the feedgrounds are operated by the Wyoming Game and Fish Department (WGFD). However, eight feedgrounds are located on lands managed by the U.S. Forest Service (USFS), which requires a permit to WGFD to conduct the operations. USGS is working with USFWS and USFS on a structured decision-making process to assess the continued use of these sites for feeding elk in light of potential CWD impacts. There are concerns that winter supplemental feeding may facilitate the spread of CWD due to higher densities of elk in the feedgrounds, and the prions that cause CWD can remain infectious in the soil creating hotspots of CWD transmission that could infect elk and deer for years to come.

Supplemental winter feeding of elk in Wyoming is done for a variety of reasons, including concerns about winter elk mortality, supporting higher elk populations for the hunting community, and decreasing the risk of disease transmission between elk and cattle.

Structured decision-making is a formal, transparent approach that breaks complex problems into simpler, more manageable parts, and helps navigate multiple objectives, trade-offs and uncertainty. The USGS scientists are both facilitating this process and assisting on technical analyses.

Contacts: Paul Cross and Jonathan Cook, USGS

Wind River Reservation Project: Identifying CWD transmission hotspots

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CWD was found in 60% of adult mule deer (60% prevalence) in the Wind River region in west-   central Wyoming during multiple recent annual statewide surveillance efforts. Prevalence of CWD in white-tailed deer in the same region is about 20%. This region is managed by the Wind River Reservation (Wind River Intertribal Council) and the Wyoming Game and Fish Department (WGFD), and the high prevalence in mule deer has prompted both management groups to improve their understanding of CWD, especially regarding the ecology and behavior of the two deer species. We will attempt to identify hotspots of CWD transmission on the landscape in the greater Wind River region. For white-tailed deer, their relatively limited movement will allow for the use of standard statistical approaches. However, mule deer are migratory so identifying discrete hotspots will be more challenging. Therefore, we will use movement, density, and disease data to refine our ability to locate CWD transmission hotspots on the landscape for mule deer. Disease data will be collected from tissue collected from hunter-harvested animals and molecularly tested for the presence for the prion that causes CWD. To track animal movement and provide the date to generate population estimates and density, mule deer will be fixed with GPS collars and tracked via aerial surveys. This study can assist the managers of the Wind River region on finding potential CWD transmission hotspots and identifying which components of the mule deer population (migrating vs. non-migrating) may be contributing more to the high CWD prevalence on the region.

Contacts: Paul Cross, USGS

Harvest and CWD

Understanding interactions between harvest and CWD transmission

Harvest is one of the major strategies used to manage the spread of CWD, yet questions remain about its effectiveness and the precise mechanisms by which it may alter CWD prevalence. We are investigating how hunting alters transmission dynamics and observed CWD prevalence, through a combination of simulation-based modeling and analysis of long-term data (in collaboration with Wyoming Fish and Game Department). Simulations will allow us to explore the different ways in which hunting could shape CWD prevalence, as well as identify what modeling approaches and data streams are needed to accurately estimate the relationships between hunting and disease transmission. These insights will be applied to a 20-year dataset from Wyoming to evaluate how harvest has impacted (and been impacted by) CWD prevalence across the state.

Contacts: Wynne Moss and Paul Cross, USGS

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

Immune responses of deer to CWD on the landscape

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The disease-causing agent of CWD, an infectious prion, does not induce a typical antibody response. Additionally, it is not clear how other aspects of the immune system of animals infected with CWD responds to the disease, but the immune system propagates and spreads prions throughout the body once they escape the initial macrophage defense—the stage where macrophages, a type of white blood cell, engulfs and potentially destroys prions. Therefore, a tradeoff between immune responses and CWD progression may exist where animals that are genetically predisposed to longer CWD incubation may exhibit poorer overall immunity. Being more susceptible to other infectious diseases could prevent these more “resistant” individuals (genotypes) from becoming more common. However, there have been no studies examining how the immune systems of individuals or populations respond to CWD in the wild.

We plan to assess immune responses primarily in mule deer from central Wyoming and white-tailed deer from southeast Minnesota using blood samples taken during GPS-collaring capture operations. We will use an assay that will indirectly measure the activity of immune mediators that promote CWD progression in deer. Additionally, we will conduct a complete blood cell count and measure levels of various white blood cells, including monocytes (macrophage precursor), which may be able to initially resist CWD infection. Better understanding how the immune system initially responds to and enables CWD infection may allow scientists and managers to better understand if animals could resist infection in certain situations and if weaker immune responses prolong CWD incubation times. Additionally, identifying variation between species and regions in their immune responses to CWD could help wildlife managers tailor their management strategies.

Contacts: Brian Dugovich and Paul Cross, USGS

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.

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