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A review of chronic wasting disease in North America with implications for Europe

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Atle Mysterud at University of Oslo
Atle Mysterud
David Edmunds at United States Geological Survey
David Edmunds
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Abstract

Cervids are keystone species in ecosystems and are associated with enormous cultural and economic value. Chronic wasting disease (CWD) is a fatal prion disease spreading in North American cervid populations. The 2016 emergence of CWD in Europe makes it urgent to understand the basics of CWD and to assess the extent to which current CWD knowledge is transferable to Europe. CWD is difficult to detect in the early stages due to very low prevalence and slow growth rates. The negative population effect of CWD is mainly due to increased female adult mortality, as infected individuals continue to reproduce. It may take decades before CWD leads to population declines. The population dynamics of mule deer are affected more by CWD than those of white-tailed deer, which in turn are more affected than those of elk, and depending on other factors limiting the populations. Species- and population-specific differences in dynamical consequences are linked to the balance among the rates of transmission, incubation period (linked to the prion protein gene, PRNP), and reproductive rates. This make it difficult to predict effects of CWD in Europe with other cervids, but the dynamic impact may be marked to cervid populations over the long term. The process of spillover across the species barrier is not well understood. Occasional spillover to moose without an apparent epizootic suggests specific conditions can limit CWD. Frequency-dependent transmission or weak density–dependent transmission makes it difficult to control CWD using density reductions through harvest and/or culling. CWD is difficult to eradicate once it becomes endemic, and it calls for immediate management actions. These actions involve extensive culling, fencing, and ceasing of wildlife feeding and are likely to cause significant controversy.
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REVIEW
A review of chronic wasting disease in North America
with implications for Europe
Atle Mysterud
1
&David R. Edmunds
2
Received: 29 January 2018 /Revised: 28 January 2019 /Accepted: 10 February 2019 /Published online: 21 February 2019
#Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
Cervids are keystone species in ecosystems and are associated with enormous cultural and economic value. Chronic wasting
disease (CWD) is a fatal prion disease spreading in North American cervid populations. The 2016 emergence of CWD in Europe
makes it urgent to understand the basics of CWD and to assess the extent to which current CWD knowledge is transferable to
Europe. CWD is difficult to detect in the early stages due to very low prevalence and slow growth rates. The negative population
effect of CWD is mainly due to increased female adult mortality, as infected individuals continue to reproduce. It may take
decades before CWD leads to population declines. The population dynamics of mule deer are affected more by CWD than those
of white-tailed deer, which in turn are more affected than those of elk, and depending on other factors limiting the populations.
Species- and population-specific differences in dynamical consequences are linked to the balance among the rates of transmis-
sion, incubation period (linked to the prion protein gene, PRNP), and reproductive rates. This make it difficult to predict effects of
CWD in Europe with other cervids, but the dynamic impact may be marked to cervid populations over the long term. The process
of spillover across the species barrier is not well understood. Occasional spillover to moose without an apparent epizootic
suggests specific conditions can limit CWD. Frequency-dependent transmission or weak density–dependent transmission makes
it difficult to control CWD using density reductions through harvest and/or culling. CWD is difficult to eradicate once it becomes
endemic, and it calls for immediate management actions. These actions involve extensive culling, fencing, and ceasing of wildlife
feeding and are likely to cause significant controversy.
Keywords Frequency-d ependent ver sus density -dependent transmissi on .Directand environmentaltransmissionroutes .Spatially
targeted harvesting .Extermination and fallowing .Salt licks and supplemental feeding .Genetics and pathology .Epizootiology
and population dynamics
Introduction
The first case of chronic wasting disease (CWD) in Europe
was diagnosed in March 2016 in a female reindeer (Rangifer
tarandus) in the Nordfjella mountains, Norway (Benestad
et al. 2016). Since then, several more CWD-infected reindeer
from the same population were detected by testing during the
2016 and 2017 hunting seasons (Viljugrein et al. 2019).
Hence, we have the first reported outbreak of CWD in
Europe. CWD was first documented in a captive mule deer
(Odocoileus hemionus) in 1967 in Colorado, USA (Williams
and Young 1980), and it appeared in wild mule deer in 1981
(Williams and Young 1992; Spraker et al. 1997;Milleretal.
2000). CWD in the wild has since spread to 25 states and,
through sales of farmed elk, has been introduced to two
Canadian provinces and to South Korea (Uehlinger et al.
2016); however, the origin of CWD in Norway remains un-
known (Benestad et al. 2016).
It is important to realize that although CWD was first iden-
tified among wild deer in 1981, it is still spreading to new
areas and continuing to increase in prevalence in most, if not
all, endemic areas. Evidence of declining populations in en-
demic areas is recently reported for white-tailed deer
(Odocoileus virginianus) (Edmunds et al. 2016) and mule deer
*Atle Mysterud
atle.mysterud@ibv.uio.no
1
Centre for Ecological and Evolutionary Synthesis (CEES),
Department of Biosciences, University of Oslo, P.O. Box 1066,
Blindern, NO-0316 Oslo, Norway
2
Natural Resource Ecology Laboratory, Colorado State University,
Fort Collins, CO 80523, USA
European Journal of Wildlife Research (2019) 65: 26
https://doi.org/10.1007/s10344-019-1260-z
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... As CWD may infect members of the cervid family, including elk, deer, and moose, it has critical implications for elk population performance and management on rangelands and elsewhere. CWD was first recognized in the 1970's at a captive deer research facility in northwestern Colorado (Williams and Young 1980), and since has spread throughout captive and free-ranging elk, deer, and moose populations across North America (Mysterud and Edmunds 2019). Control efforts to date have largely been unsuccessful at reducing the spatial spread and prevalence of CWD in free-ranging elk populations (Uehlinger et al. 2016). ...
... The effect of CWD on elk population demography is primarily due to reduced adult female survival rates, as infected individuals will continue to reproduce (Mysterud and Edmunds 2019). Depending on the prevalence and other factors interacting to influence adult female survival rate, CWD may have variable effects on elk population performance (Monello et al. 2014;Mysterud and Edmunds 2019). ...
... The effect of CWD on elk population demography is primarily due to reduced adult female survival rates, as infected individuals will continue to reproduce (Mysterud and Edmunds 2019). Depending on the prevalence and other factors interacting to influence adult female survival rate, CWD may have variable effects on elk population performance (Monello et al. 2014;Mysterud and Edmunds 2019). For example, in the Rocky Mountain elk population, CWD prevalence rates exceeding 13% have the potential to decrease population growth (Monello et al. 2014). ...
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... Chronic wasting disease (CWD) is a communicable disease found in wild and captive deer, elk, moose, and other members of the family Cervidae. As of January 2024, CWD is known to exist in the United States, Canada, and several Nordic nations' free-ranging cervid herds (Mysterud and Edmunds 2019). CWD belongs to a disease family that includes other transmissible spongiform encephalopathies (TSEs) such as bovine spongiform encephalopathy and Creutzfeldt-Jakob disease in humans. ...
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Pathologic and biochemical characterization of PrPSc from elk with PRNP polymorphisms at codon 132 after experimental infection with the chronic wasting disease agent
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Scientific opinion on chronic wasting disease (II)
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This article examined relationships between proximity to chronic wasting disease (CWD) and perceived risk and trust. The sample included 1,606 hunters in one of 10 northern Illinois counties with CWD, 1,958 hunters in a non-CWD county adjacent to these counties with CWD, and 2,099 hunters from the remaining non-CWD counties in Illinois. Compared to hunters in non-CWD counties, those in CWD counties were hypothesized to: (a) perceive more risk of CWD to humans, (b) perceive more risk of CWD to deer, (c) report less trust in the Illinois Department of Natural Resources (IDNR) CWD information, and (d) have less trust in the IDNR management of CWD. The first two hypotheses were not supported, as hunters in CWD counties perceived less risk to humans and deer than did respondents in non-CWD counties. Hunters in CWD counties, however, were less trusting of the IDNR information and management compared to the other hunters.
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Contact Tracing for the Control of Infectious Disease Epidemics: Chronic Wasting Disease in Deer Farms
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Contact tracing is a crucial component of the control of many infectious diseases, but is an arduous and time consuming process. Procedures that increase the efficiency of contact tracing increase the chance that effective controls can be implemented sooner and thus reduce the magnitude of the epidemic. We illustrate a procedure using Graph Theory in the context of infectious disease epidemics of farmed animals in which the epidemics are driven mainly by the shipment of animals between farms. Specifically, we created a directed graph of the recorded shipments of deer between deer farms in Pennsylvania over a timeframe and asked how the properties of the graph could be exploited to make contact tracing more efficient should Chronic Wasting Disease (a prion disease of deer) be discovered in one of the farms. We show that the presence of a large strongly connected component in the graph has a significant impact on the number of contacts that can arise.
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A method that accounts for differential detectability in mixed samples of long-term infections with applications to the case of Chronic Wasting Disease in cervids
Article
Surveillance of wildlife diseases is logistically difficult, and imperfect detection is a recurrent challenge for disease estimation. Using citizen science can increase sample sizes, but it is associated with a cost in terms of the anatomical type and quality of the sample. Additionally, biological tissue samples from remote areas lose quality due to autolysis. These challenges are faced in the case of emerging chronic wasting disease ( CWD ) in cervids. Here, we develop a stochastic scenario tree model of diagnostic sensitivity, allowing for a mixture of tissue sample types (lymph nodes and brain) and qualities while accounting for different detection probabilities during the CWD infection, lasting 2–3 years. We apply the diagnostic sensitivity in a Bayesian framework, enabling estimation of age‐class‐specific true prevalence, including the prevalence in latent, recently infected stages. We provide a simulation framework to estimate the sensitivity of the surveillance system (i.e., the probability of detecting the infection in a given population), when detectability varies among individuals due to different disease progression. We demonstrate the utility of our framework by applying it to the recent emergence of CWD in a European population of reindeer. We estimated apparent CWD prevalence at 1.2% of adults in the infected population of wild reindeer, while the true prevalence was 1.6%. The sensitivity estimation of the CWD surveillance was performed in an adjacent small ( c . 500) and a large ( c . 10,000) reindeer population, demonstrating low certainty of CWD absence. Our method has immediate application to the mandatory testing for CWD in EU countries commencing in 2018. Similar approaches that account for latent stages and a serial disease progression in various tissues with a temporal pattern of diagnostic sensitivity may enhance the estimation of the prevalence of wildlife diseases more generally.
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A reindeer cull to prevent chronic wasting disease in Europe
Article
  • Jul 2018
  • Nat. Ecol. Evol.
The emergence of chronic wasting disease among wild reindeer in Norway triggered the decision to eradicate an entire population of more than 2,000 animals. The cull, now complete, was a tremendously difficult process both politically and practically.
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