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Prevalence and Effects of Chronic Wasting Disease in Elk from Rocky Mountain National Park

Posted Apr 05 2012 11:22pm
Prevalence and Effects of Chronic Wasting Disease in Elk from Rocky Mountain National Park

Ryan Monello Biological Resource Management Division National Parks Service N. Thompson Hobbs Natural Resource Ecology Laboratory Department of Ecology Colorado State University Jenny G. Powers Biological Resource Management Division National Park Service Terry R. Spraker Colorado State Diagnostic Laboratory College of Veterinary Medicine Colorado State University Margaret A. Wild Biological Resource Management Division National Park Service

Chronic wasting disease (CWD) can have long-term, negative impacts on deer populations, but there is little known about the ecology of CWD in free-ranging elk (Cervus elaphus). We placed radio-collars on 136 adult female elk in Rocky Mountain National Park (RMNP) as part of a three-year study that measured the efficacy of rectal biopsies to diagnose prion infection and the impact of CWD on elk survival and population growth. Elk with biopsies that tested positive via immunohistochemistry (IHC) were euthanized, and postmortem samples were examined with IHC. Survival was monitored on a weekly basis and 20-34 study animals were resampled and euthanized annually. Specificity of rectal biopsies was 100%, while sensitivity was 74% when three or more follicles were obtained from the biopsy. Rectal biopsy test results were similar to brainstem samples, but neither tissue contained prions in the earliest stages of infection that were only detected in retropharyngeal lymph nodes. Minimum prevalence (% of elk infected) was estimated to be 9.9% (95% credible limits (CI) = 5.7, 15.7) based on rectal biopsies, but this estimate rose to 12.9% (CI = 8.0, 19.1) when we included four elk that were likely misdiagnosed at initial capture. Following removal of all known individuals with CWD, the annual survival rate was relatively high during the initial year of the study, but declined in subsequent years due to consistent increases in CWD-related mortalities (2008 survival = 0.97 [CI: 0.93, 0.99], 2009 = 0.90 [CI: 0.83, 0.95], 2010 = 0.85 [CI: 0.75, 0.93]). These results suggest that 1) rectal biopsies can be a useful research tool, but can miss elk in the earliest stages of prion infection; and 2) CWD can reduce the survival of adult females and slow the population growth of high-density elk herds.

Cervus elaphus, chronic wasting disease, Colorado, elk, mortality, prevalence, prion, survival

National Wildlife Health Center Enhanced Surveillance Strategies for Detecting and Monitoring Chronic Wasting Disease in Free-Ranging Cervids

Open-File Report 2012–1036


In addition to locations of known CWD-positive individuals, other spatial risk factors related to CWD exposure should be considered. For example, the risk of free-ranging animals being exposed to CWD is likely greater in areas where captive cervid facilities have or had CWD-positive animals. Current evidence indicates that CWD infection rates are much higher in captive facilities than in wild populations (Keane and others, 2008), and perhaps this is driven by environmental contamination (Miller and others, 2006). This higher rate of infection in captive animals can increase the risk of disease exposure to surrounding wild populations. Furthermore, movement of infectious animals, carcasses, or other materials across the landscape, naturally or with human assistance, likely increases the risk to uninfected populations. The frequent movement of farmed elk (Cervus elaphus) and deer between production facilities, the concentration of infected animals on some facilities, and the possibility of their escape into the wild increases the risk of spreading CWD to uninfected populations of free-ranging animals. Because the infectious prions may persist in the environment for long periods, the introduction of either captive or free-ranging uninfected animals into a contaminated environment could increase their risk of infection. For example, locations from which sheep have been removed may remain contaminated with scrapie agent for more than 15 years (Georgsson and others, 2006). In a similar manner, translocation of cervids from areas that have not been documented to be CWD-free could pose a risk of disease introduction. In this situation, the risk of introduction is likely related to the probability of infected animals being moved and their ability to spread CWD to other susceptible animals or into the environment. Thus, surveillance on and around cervid farms or free-ranging populations that have received animals from known CWD areas and bordering jurisdictions with CWD-positive animals can increase the likelihood of disease spread. Additional risk factors, such as the presence of scrapie in sheep populations that are sympatric with deer and elk (Greenlee and others, 2011), feeding of animal protein to cervids (Johnson, McKenzie, and others, 2011), baiting and feeding programs (Thompson and others, 2008), or other environmental factors also may be considered, although their roles in CWD epidemiology has not been clearly established.


Baiting or feeding, which artificially increases concentrations of animals, may increase the chance of disease spread through direct contact among animals or indirect contact with environmental contamination (Thompson and others, 2008; Mathiason and others, 2009; Tamguney and others, 2009; Haley and others, 2011). Thus, variation in density of deer or infected deer across the landscape is another important spatial risk factor to consider when conducting disease surveillance or monitoring (Joly and others, 2009).


It has also been recognized that targeted surveillance of individuals demonstrating clinical signs consistent with CWD infection results an increased probability of detecting CWD. In one study, 66 percent and 43 percent of submitted deer and elk exhibiting clinical signs of CWD, respectively, were diagnosed as CWD-positive compared to 5 percent and 0.5 percent of randomly sampled deer and elk submitted for testing (Miller and others, 2000). Therefore, exhibition of clinical signs of CWD is a clearly an attribute that increases an individual’s likelihood of having CWD and is a demographic risk factor that can be exploited to increase surveillance efficiency. Targeted surveillance and investigation of clinical animals also has the added benefit of detection of other important wildlife diseases with similar clinical signs (Miller and others, 2000; Samuel and others, 2003).

Other demographic risk factors are less well understood. For example, there is evidence that genetics plays a role in individual susceptibility and rate of disease progression. Similar to other TSEs, polymorphisms of the prion protein gene (PRNP) may moderate individual susceptibility to and progression of CWD infection of elk, mule, and white-tailed deer (O’Rourke and others, 2004; Spraker and others, 2004; Jewell and others, 2005; Fox and others, 2006; Hamir and others, 2006; Goldmann, 2008; Keane and others, 2008; Perucchini and others, 2008). Therefore, it appears that certain individuals are innately at higher risk of CWD infection based solely on their PRNP genotype. For example, Wisconsin white-tailed deer with the PRNP genotype G96G have approximately four times higher rate of infection and 8 months shorter survival after infection compared to G96S deer (Robinson and others, 2012). However, unlike other TSEs, there is no evidence that any of the PRNP genotypes in wild cervids are immune to CWD infection.


Finally, high population density, which also can be considered a spatial risk factor, is generally believed to create increased risk of disease transmission through higher direct or indirect contact rates (Swinton and others, 2001; Ramsey and others, 2002). This is the basis for population reduction strategies used by many wildlife management agencies for CWD management in free-ranging cervids (Williams and others, 2002; Joly and others, 2003; Williams, 2005; Joly and others, 2006). The actual transmission route of CWD is not known, however, experimental evidence from captive cervids suggests that CWD infection occurs via horizontal transmission through both direct and indirect contact between susceptible and infected individuals (Miller and Williams, 2003; Williams and Miller, 2003), and both kinds of contact can be influenced by density. Experimental inoculation with blood, urine, feces, and saliva from CWD-infected individuals has been shown to provide viable routes of transmission, suggesting direct contact with any of these infectious materials could act as a route of infection (Miller and others, 2004; Mathiason and others, 2006; Miller and others, 2006; Trifilo and others, 2007; Safar and others, 2008; Haley and others, 2009; Mathiason and others, 2009; Tamguney and others, 2009; Haley and others, 2011). Indirect contact may play an important role in transmission dynamics via environmental contamination, because the CWD agent can persist in contaminated systems for 2 or more years (Miller and others, 2004), and if CWD is similar to scrapie, it may persist for 15 or more years (Georgsson and others, 2006). For captive cervids, the most likely route of exposure is orally through foraging activities in the immediate vicinity of fresh and decomposed carcasses or ingestion of fresh and residual excreta from infected individuals (Miller and others, 2004; Trifilo and others, 2007; Safar and others, 2008; Mathiason and others, 2009). However, the relative importance of direct and indirect transmission of CWD in wild cervids has not been determined. As previously mentioned, certain soil types can also increase oral infectivity of TSEs, which may allow environmental contamination to be problematic even in the presence of relatively low doses of the infective agent (Johnson and others, 2007). Thus, it is likely density of infected cervids can contribute to increased indirect contact rate between susceptible and infected individuals or contact with an environmental reservoir. However, it is unclear to what the extent density influences these processes.



We have presented a wide range of risk factors that may be considered when designing surveillance or monitoring programs. Although this is not an exhaustive list and undoubtedly other factors not yet described will come to light, the risk factors and associated references detailed herein provide a useful starting point. Many jurisdictions currently collect information on many of these factors, especially for harvested cervids. Other data related to spatial risk factors may be readily available within Geographic Information Systems (GIS). Thus, the use of the risk factors in surveillance and monitoring activities is a natural progression in continued improvement of these activities.

For jurisdictions lacking quantitative information on various risk factors, we recommend collaborating with similar entities that have available information and utilizing their data to incorporate risk factors into disease-management activities. In addition, even if information is limited or unavailable for some of the risk factors described, use of the information that is available for the remaining factors may provide gains in efficiency. However, we caution that, if possible, risk factors related to CWD infection should also consider potential differences in species of interest, differences in harvest strategies among areas, if CWD is in an early or advanced stage of epizootic (low vs. high prevalence), and how different cervid ecology and habitat features might affect estimate risk factors. At the current time, little is known about how many of these features might affect CWD prevalence and risk of infection.

Evaluation of risk factors helps to focus resources on locations or target populations with a greater likelihood of being infected and increases the efficiency of surveillance and monitoring efforts. Agencies charged with managing this disease should continue to look for efficient ways to conduct their activities. Identifying, understanding the importance of, and incorporating risk factors into surveillance and monitoring activities are potential means of meeting this need for increased efficiency.

Chronic Wasting Disease CWD CDC REPORT MARCH 2012

Saturday, February 18, 2012

Occurrence, Transmission, and Zoonotic Potential of Chronic Wasting Disease

CDC Volume 18, March 2012



CWD has been identified in free-ranging cervids in 15 US states and 2 Canadian provinces and in 100 captive herds in 15 states and provinces and in South Korea (Figure 1, panel B).



Long-term effects of CWD on cervid populations and ecosystems remain unclear as the disease continues to spread and prevalence increases. In captive herds, CWD might persist at high levels and lead to complete herd destruction in the absence of human culling. Epidemiologic modeling suggests the disease could have severe effects on free-ranging deer populations, depending on hunting policies and environmental persistence (8,9). CWD has been associated with large decreases in free-ranging mule deer populations in an area of high CWD prevalence (Boulder, Colorado, USA) (5).

SNIP... see map ;

full text ;

see much more here ;

Thursday, February 09, 2012

Colorado Farm-Raised Deer Farms and CWD there from 2012 report Singeltary et al


Tuesday, December 20, 2011


> > > The CWD infection rate was nearly 80%, the highest ever in a North American captive herd.

Despite the five year premise plan and site decontamination, The WI DNR has concerns over the bioavailability of infectious prions at this site to wild white-tail deer should these fences be removed. Current research indicates that prions can persist in soil for a minimum of 3 years.

However, Georgsson et al. (2006) concluded that prions that produced scrapie disease in sheep remained bioavailable and infectious for at least 16 years in natural Icelandic environments, most likely in contaminated soil.

Additionally, the authors reported that from 1978-2004, scrapie recurred on 33 sheep farms, of which 9 recurrences occurred 14-21 years after initial culling and subsequent restocking efforts; these findings further emphasize the effect of environmental contamination on sustaining TSE infectivity and that long-term persistence of prions in soils may be substantially greater than previously thought. < < <


Thursday, February 09, 2012



Saturday, February 04, 2012

Wisconsin 16 age limit on testing dead deer Game Farm CWD Testing Protocol Needs To Be Revised

Chronic Wasting Disease National Program for Farmed and Captive Cervids Update

Patrice N. Klein, National Center for Animal Health Programs, USDA-APHISVS

In FY2010, APHIS received approximately $16.8 million in appropriated funding for the CWD Program, including $1.0 million in congressional earmarks. The FY2011 President’s proposed budget for the CWD Program is $14.2 million (exclusive of any congressional earmarks). In the first quarter of FY2011, the federal government is operating on a Continuing Resolution based on a quarterly percentage of the FY10 budget. CWD Rule Update: Public comments received on the proposed amendments to the 2006 CWD rule were categorized, reviewed, and responses were drafted. Issues that may impact the amended final rule and CWD Program implementation include the President’s Memo on federal preemption (May 20, 2009), budgetary constraints, and ongoing need for additional research to better understand the science for prevention and control of CWD. A draft of the amended CWD final rule is in clearance in November 2010. Surveillance testing: Through FY2009, VS conducted surveillance testing on more than 23,000 farmed and captive cervids by the immunohistochemistry (IHC) standard protocol. In FY2010, approximately 20,000 farmed and captive cervids were tested by IHC for CWD with funding to cover lab costs provided through NVSL. Status: CWD was detected in one captive white-tailed deer (WTD) herd in Missouri in February 2010. To date, 50 farmed/captive cervid herds have been identified in 11 states: CO, KS, MI, MN, MO, MT, NE, NY, OK, SD, WI. Thirty-seven were elk herds and 13 were WTD herds. At this time, six CWD positive elk herds remain in Colorado and one WTD herd remains in MO. VS has continued to offer indemnity for appraised value of the animals and to cover costs of depopulation, disposal, and testing of CWD-positive and exposed herds. Indemnity is provided based on availability of federal funding.


Controlling Disease at the Fence: Research Questions, Answers, and on to More Questions

Kurt VerCauteren, National Wildlife Research Center, USDA-APHIS-WS

In recent years the National Wildlife Research Center has collaborated with many privately owned elk and deer producers to investigate many aspects regarding the potential for disease transmission between freeranging and captive cervids. A suite of studies began with a fencelineinteraction evaluation designed to determine if and to what extent interactions occurred along perimeter fences. We found through 1 year of video monitoring that interactions between captive and free-ranging whitetailed deer (Odocoileus virginianus) were relatively rare (2 direct contacts and 7 indirect contacts). Interactions between captive and free-ranging elk (Cervus elaphus), though, were relatively common (77 direct contacts and 274 indirect contacts). To address this issue, we proceeded to design and evaluate a cost-effective baited-electric fence that could be added to an existing single perimeter fence to minimize potential interactions. Our case study documented that once exposed to the electric fence individual elk learned to respect it and were completely deterred thereafter. The ambiguous question of how high white-tailed deer can jump was next on our list of pursuits to further evaluate risk associated with perimeter fences.

Following a controlled evaluation involving 43 white-tailed deer motivated to jump progressively higher fences, we determined that a 2.1-m-high fence presents a considerable barrier. We also teamed up with colleagues to develop the rectal biopsy antemortem test for identifying CWD-infected individuals, collecting over 1,500 rectal biopsies from captive cervids to date. We have incorporated the procedure into our research and continue to work toward assessing its utility relative to management. To prepare for instances when disease is introduced into the wild at a pointsource, we initiated a study evaluating rapid containment of white-tailed deer and demonstrated the efficacy of 2.1-m-high polypropylene mesh fence for emergency containment. A study we hope to do will document how captive white-tailed deer respond following “escape” from a captive deer facility. The study would give us an understanding of how easily these deer can be recaptured and how readily they integrate into the local free-ranging deer herd. The progression of research that we have conducted to date has provided insight into what occurs along perimeter fences at captive cervid facilities and is enabling producers and management agencies to make more informed decisions relative to protecting valuable resources inside and outside fences. We will briefly discuss these studies and more.

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