PROJECT GOAL: Develop practical and effective methods for managing disease and damage involving wild and domestic ungulates.
Project Accomplishments 2010
Chronic Wasting Disease
The spread of chronic wasting disease (CWD) in wild and captive cervids is of great nationwide concern. More research is needed to fill information gaps about disease transmission at the interface between wild and domestic cervids. CWD infects elk, white-tailed deer, mule deer, and moose, but is not known to naturally infect other species of wildlife (including predators and scavengers), livestock, or humans. There is no treatment for CWD, and typically, the disease is fatal in cervids. Realized and perceived CWD threats have significant implications for federal and state wildlife management agencies, domestic cervid farmers, hunters, and businesses and economies reliant on deer and elk. In addition, these groups need additional and improved tools and management techniques to reduce the transmission, prevalence, and persistence of CWD in wild and captive cervids.
Elk Age and Sex Influences on CWD Rectal Biopsies—Rectal lymphoid tissue can be used for detecting CWD in Rocky Moutain elk (Cervus elaphus nelsoni). In fact, this method is the only practical live test for CWD in elk at this time. During a study conducted between 2005 and 2008, NWRC researchers took 1,361 rectal biopsies from captive elk to determine if the number of rectal lymphoid follicles in animals decreases with respect to age and sex relative to the diagnosis of CWD. Rectal tissues were then stained with a monoclonal antibody that selectively stains the abnormal isoform of the prion protein associated with CWD.
The results of this study showed that the number of lymphoid follicles obtained from typical biopsy tissues decreased with the age of the animal. The acceptable number of lymphoid follicles for detection of CWD was not considered to be a problem for elk up to 8.5 years of age, but for elk over 8.5 years of age, the follicle count was considered to be low. The sex of the animal had no affect on the number of lymphoid follicles observed in each age group. Based on these results, the researchers concluded that the rectal biopsies were an accurate test to diagnose preclinical stages of CWD in elk, especially for elk less than 8.5 years of age.
Predicting CWD Progression in Elk—In a recent study, National Wildlife Research Center (NWRC) researchers examined sections of brain stem, lymph node, and tonsil from approximately 300 free-ranging and 15,000 ranch-raised adult Rocky Mountain elk (Cervus elaphus nelsoni) for the presence of the abnormal isoform of the prion protein (PrPCWD) that has been associated CWD. A total of 321 (24 free-ranging and 297 ranch-raised) elk were found to be positive. The researchers then selected 60 of the positive ranch-raised elk and all of the 24 free-ranging elk to be the basis for the development of a detailed scoring technique of the obex (brain stem at the level where the fourth ventricle converges into the central canal of the spinal cord). NWRC scientists assisted colleagues from Colorado State University, DOI’s National Park Service, USDA’s Agricultural Research Service, the U.S. Geological Survey (USGS), and the Canadian Food Inspection Agency to develop the technique, called the “obex score,” to predict in elk which structure or regions of the brain, spinal cord, and extra neural tissues contain PrPCWD.
It is expected that PrPCWD spreads throughout the obex of the brain stem at a rate similar to the movement of PrPCWD throughout the central nervous system and extra neural tissues. Results suggest that PrPCWD and the severity of spongiform degeneration have a unique and consistent pattern of progression through a section of brain stem at the level of the obex in both naturally occurring and experimentally induced CWD. Therefore, the obex score has potential usefulness as a basis for evaluating the presence of PrPCWD in peripheral tissues and brain. Current studies are evaluating approximately 100 peripheral tissues and 75 neuro-anatomical locations of the brain and spinal cord in 36 free-ranging and ranch-raised elk with naturally occurring CWD and known incubation times. These results will be compared with corresponding obex scores.
Concurrent work with live animals is relating the level of CWD infection with changes in behavior. Cumulative results could lead to strategies for detecting infected animals before they show clinical signs, which could be useful in the treatment of infected individuals and management of CWD.
Distribution and Epizootiology of CWD in Nebraska Deer—Western Nebraska is considered part of the core endemic area of CWD, yet little is known about prevalence rates or the factors affecting the distribution of CWD in this area. NWRC researchers used data on the occurrence of CWD collected from 2000 to 2007 throughout Nebraska to calculate prevalence rates and investigate the role that key spatial, temporal, demographic, and environmental factors have on the distribution of this disease. Researchers conducted analyses at two spatial scales, including the Panhandle region of western Nebraska and Statewide.
Results show that the dynamics of CWD were similar between the different spatial scales. CWD was more prevalent in mule deer (Odocoileus hemionus) than in white-tailed deer (Odocoileus virginianus), in male deer than in female deer, and in adult deer than in fawns. Overall prevalence has increased from 0.3 to 1.4% in the Panhandle and from 0.2 to 0.5% statewide. The sex of the animal and the interaction of latitude and longitude had the most influence when predicting CWD occurrence in Nebraska at both spatial scales. Age, year collected, and soil texture were also predictors. These results concur with studies conducted in other areas of the CWD core endemic area, suggesting that CWD dynamics are governed by similar processes throughout the disease’s range.
Avian Scavengers as Vectors of Prion Disease—Mechanisms for the spread of CWD in North American deer and other cervids are not completely understood. NWRC researchers hypothesize that avian scavengers may play a role in translocating CWD in the wild, potentially encountering CWD-infected carcasses, consuming infected tissue, and transporting it over long distances before depositing feces. In a recent study, researchers inoculated 100 mice with fecal extracts obtained from American crows (Corvus brachyrhynchos) that were force-fed material infected with mouse scrapie (PrPSc). These mice showed severe neurological dysfunction 196 to 231 days post inoculation and tested positive for PrPSc. These results demonstrate that a common, migratory North American scavenger can pass infective prions in feces and, therefore, could play a role in the geographic spread of CWD in the environment.
Impact of Flooding on Deer Movements—Few studies have examined the effects of flooding on the habitat use, movements, and survival of white-tailed deer (Odocoileus virginianus). In June 1996, the Missouri River overflowed its banks and inundated much of the floodplain in eastern Nebraska and western Iowa. The flood occurred 3 weeks after the peak of the fawning season and was concurrent with a study evaluating the home range activity and movements of female white-tailed deer in a suburban natural area. NWRC, University of Nebraska, and McNeese State University scientists monitored the locations of 22 radio-marked, female white-tailed deer inhabiting eastern Nebraska lowlands and determined mean size of use-areas, use-area overlap, and movements of deer 30 days before, during, and after the flood.
The results showed that over 75% of the deer abandoned their pre-flood use-areas and moved short (less than 400 meters) distances to elevated areas. The average distance moved from before-during the flood period was 0.69 kilometers and from during-after flood period was 0.32 kilometers. The mean size of use-areas was similar from before (100 ha) to during (103 ha) the flood, but decreased by 50% to 54 ha after the flood. The overlap between before- and during-flood use-areas was 35%, while during- and after-flood use-areas overlapped 53%. However, these distances were biased by four deer that moved greater than 900 meters to avoid floodwaters, three of which never returned to their pre-flood use-areas. Once these were removed from the data set, mean movement distances were 0.37 kilometers (before-during) and 0.11 kilometers (during-after); mean use-area size was 106 ha (before), 56 ha (during), and 41 ha (after); use-area overlap was 43% (before-during) and 59% (during-after). Doe:fawn ratios in 1996 (1:0.4) were considerably lower after the flood than in 1995 (1:1.5). Female deer showed strong fidelity to pre-established use-areas. Flooding had little effect on adult deer survival. The combination of flood waters and loss of quality forage most likely explain the decline in fawn numbers . These data provide important information towards understanding the impact of severe weather and flooding on white-tailed deer populations and management strategies .
Livestock Protection Dogs—Livestock producers, particularly those with smaller scale operations, worldwide are often confronted with the challenge of reducing livestock losses to predators and wildlife-transmitted diseases. In the Great Lakes Region of the United States, this conflict has increased in recent years, as gray wolf (Canis lupus) populations have recovered and burgeoning populations of white-tailed deer (Odocoileus virginianus) have served as a wildlife reservoir for bovine tuberculosis (Myobacterium bovis; TB). One potentially valuable, nonlethal tool for protecting livestock against such threats is the use of livestock protection dogs (LPDs).
During 2007 and 2008, NWRC scientists and colleagues from Central Michigan University conducted field experiments to evaluate the effectiveness of LPDs for excluding wolves, coyotes (C. latrans), white-tailed deer, and medium-sized predators (e.g., raccoons, skunks, foxes) from livestock pastures. Scientists placed LPDs on six cattle farms (the treatment group) and monitored wildlife use on the farms along with three control farms, determining the amount of time deer spent in livestock pastures by direct observation. In the livestock pastures protected by LPDs, there was reduced use by all species of wildlife compared to control pastures not protected by LPDs. Most notably, white-tailed deer spent less time in livestock pastures protected by LPDs compared to control pastures not protected by LPDs.
This research supports the theory that LPDs can be an effective management tool for reducing livestock predation and disease. Based on these findings, NWRC supports the use of LPDs as a proactive management tool that producers can implement to minimize the threat of livestock depredations and the transmission of disease from wildlife to livestock. LPDs also may be useful as a more general conservation tool for protecting valuable wildlife, such as ground-nesting birds, that use livestock pastures and are impacted by predators using these pastures.
Goal and Objectives
Chronic Wasting Disease