Project Accomplishments 2011
Bovine tuberculosis (bTB) and chronic wasting disease (CWD) are national and international issues of concern for citizens and agencies relative to livestock and wildlife disease issues and management. A primary focus of APHIS is protecting the health of livestock, including captive cervids, realizing that the health of wild cervids affects that of livestock, and vice versa. Research in this area is needed to address scientific questions that will lead to a better understanding of the diseases and to develop means to manage and control them. NWRC researchers focus most of their effort on studies that pertain to the interface between free-ranging cervids and livestock (including captive cervids). These studies are designed to be applicable in free-ranging and domestic settings. Through novel research, including development of live-animal tests, vaccines, techniques to improve separation and prevent transmission, decontamination, and risk modeling the NWRC is filling a unique niche and developing needed knowledge that is being used to address issues associated with bTB and CWD.
Reducing fence-line contact with electric fencing Fence-line perimeters are focal sites for interaction between farmed and wild cervids. Direct and indirect contact through fences at cervid farms with only a single perimeter fence may play a role in transmission of diseases such as bTB or CWD. NWRC scientists examined effectiveness of a baited electric fence, as an addition to an existing single woven-wire fence (2.4 m high), for altering behavior and reducing fence-line contact between elk ( Cervus elaphus). They used a video-surveillance system to monitor a 20-m-long test fence area at an elk ranch in north-central Colorado, USA. Twenty-six trials (11 without electric fence and 15 with electric fence during) were conducted with different levels of motivation for contact between groups of elk separated by the test fence. Levels of motivation included separating rutting adult males from adult females, separating calves from their dams, and placing supplemental feed near the test fence. An electric fence was erected in pen A containing a test group of elk while pen B contained the attractant group. At the start of each trial that the electric fence was present, the fence was baited with molasses to attract elk to the fence and encourage them to contact it with their oral-nasal region and receive a shock (aversive conditioning). During this study, 22 of 23 elk exposed to the electric fence were completely deterred. This approach targets behavior modification of farmed elk routinely exposed to the electric fence, not wild elk that may occasionally approach from the outside. These results suggest that adding a baited-electric fence inside an existing woven-wire-fenced enclosure has potential to provide a cost-effective means to minimize contacts between farmed and wild elk. (/wildlife_damage/nwrc/publications/11pubs/fischer111.pdf)
Iophenoxic acid derivatives and rodamine B as biomarkers of white-tailed deer — Targeted oral vaccination of free-ranging white-tailed deer has been proposed as a tool for reducing prevalence of bovine tuberculosis and risk of transmission between deer and cattle. Biomarkers could be used prior to vaccine delivery to estimate population proportion coverage for different oral delivery methods, and concurrently with vaccine delivery to differentiate between deer exhibiting titer response due to natural exposure to Mycobacterium bovis (biomarker not present) versus vaccine (biomarker present). Previous evaluations of iophenoxic acid (IPAs) and rodamine B (RB) suggest promise for these applications but were not directly applicable.
The NWRC is conducting research with the following objectives: 1) develop a statistical model of dose-response-time relationship for 3 IPA derivatives and evaluate precision of using these relationships for inverse prediction of dose ingested given approximate interval between ingestion and post-delivery blood sampling of captured animals; 2) estimate time required for IPA concentrations in blood plasma to drop below detectable levels to assess risk of humans consuming hunter-harvested meat from previously biomarked deer; 3) evaluate RB as a biomarker of facial whiskers in white-tailed deer and estimate detection probability of RB over time.
Methods for delivering bovine tuberculosis vaccine to free-ranging white-tailed deer — Targeted oral vaccination of free-ranging white-tailed deer has been proposed as a tool for reducing prevalence of bovine tuberculosis and risk of transmission between deer and cattle. Researchers and managers from ARS National Animal Disease Center (NADC), Michigan Department of Natural Resources and Department of Agriculture and Rural Development, APHIS Veterinary Services and APHIS Wildlife Services (Michigan), and National Wildlife Research Center are collaborating to develop a viable approach for oral vaccine delivery. Efforts are ongoing to develop and evaluate prototype vaccine delivery units (VDU) that are compatible with carrying and protecting vaccine, as well as attractive and palatable to free-ranging deer. It is necessary to understand how potential VDUs will be received by wild deer and nontarget animals and to determine rate of degradation of vaccine potency under natural environmental conditions. Results from preliminary deployment of first-generation VDU (without vaccine) in northern Michigan during January and February 2012 will lead to refinements of the VDU and delivery methods to improve detection and uptake by deer. Results of a concurrent study of vaccine-infused VDUs in winter 2012 will quantify rate of degradation of vaccine subjected to weathering during 12 weeks under different plant overstory and environmental exposure conditions. Trials of modified VDUs are planned for winter 2013.
Infectivity of prions following ingestion and excretion from Coyotes ( Canis latrans) — CWD is a transmissible spongiform encephalopathy found naturally in free-ranging mule deer ( Odocoileus hemionus), white-tailed deer ( Odocoileus virginianus), Rocky Mountain elk ( Cervus elaphus nelsoni), and moose ( Alces alces). Natural transmission of the disease can occur directly, animal-animal or indirectly from contamination from the environment. When a diseased animal dies in the environment insect, avian, and mammalian scavengers eat the infected carcass. The primary carnivore scavengers of white-tailed deer are coyotes, which act as an intermediate host in diseases such as Echinococcosis granulosus tapeworm, or hydatid disease and canine parvovirus. Infected material is ingested and eggs or virus is shed in the feces, which is then inadvertently ingested by herbivores during grazing. With the understanding that coyotes scavenge deer carcasses, the ability of disease to be translocated in feces, and the persistent nature of CWD, it therefore seems plausible that CWD could be disseminated in the same way as other diseases. Experiments by NWRC scientists have revealed that feces from crows, another common scavenger, fed scrapie-positive (another type of transmissible spongiform encephalopathy) material could transmit disease to transgenic mice. To test of the ability of coyotes to spread CWD in their feces after ingestion of CWD-positive material, an experiment using transgenic mice is underway. Feces were collected from coyotes before and three days after ingestion of a small amount of CWD-infected elk brain material. The collected feces were prepared for inoculation into a transgenic mouse model susceptible to CWD. Data from the study thus far supports the hypothesis that coyotes can disseminate CWD in their feces for several days after ingestion of CWD-positive material, participating in the distribution of CWD-infectious material throughout the environment.
Intranasal dust inoculation of chronic wasting disease in white tailed deer ( Odocoileus virginianus) — Chronic wasting disease (CWD) is a persistent problem in both wild and captive North American cervid populations. This disease continues to spread and cases are found in new areas each year. Indirect transmission can occur via the environment and is thought to occur by oral and/or intranasal routes. Oral transmission has been experimentally demonstrated and although intranasal transmission has been postulated, it has not been tested in a natural host. Prions have been shown to strongly adsorb to clay particles and upon oral inoculation the prion/clay combination exhibits increased infectivity in rodent models. Deer and elk undoubtedly inhale dust while foraging and while performing rut behaviors. NWRC scientists hypothesized that dust particles may be a viable mode of intranasal CWD exposure. To test this hypothesis, CWD-positive brain homogenate was mixed with montmorillonite clay, dried, re-powdered and intranasally inoculated into white tailed deer once a week for 6 weeks. The findings of this study demonstrate that CWD can be efficiently intranasally transmitted utilizing montmorillonite dust particles as a carrier and that the intranasal route is a viable route of exposure. This study filled in a key missing piece of information regarding routes of transmission in deer.
Reducing transmission of bovine tuberculosis from wildlife to cattle in Michigan — The incidence of bTB in both wildlife and cattle continues to be a challenging issue in the northeastern portion the Lower Peninsula of Michigan. Several state and federal agencies are working together to combat disease transmission by evaluating each individual cattle or dairy production facility and prescribing specific mitigation measures (e.g., fencing stored feed, excluding cattle from deer habitat) to minimize potential for transmission. To assess potential transmission among wildlife and cattle, NWRC researchers designed a study to monitor direct and indirect interactions that may pose risk for disease transmission. Using proximity loggers (electronic devices that emit and receive radio signals and record time and date of occurrences) installed at cattle-related resources and deployed on cattle, deer, raccoon, and opossum, interactions between individuals and visitation to resources will be monitored. Researchers also intend to examine the effects of applied mitigation measures by comparing proximity logger data from before and after applying such measures.
The study was initiated in winter 2012 on 6 farms including 3 dairies and 3 beef-cattle operations. A target number of 4 deer proximate to each farm are being monitored by both proximity loggers and Global Positioning System (GPS) collars to assess movements both on and away from cattle operations. Similarly, a target of 4 opossum and 4 raccoon at each farm are being monitored with proximity loggers as well as telemetry collars to enable researchers to locate the animals on the landscape anytime. Motion-activated cameras are also on farms collecting supplemental information from animals not outfitted with data collection devices. The study is scheduled to continue through June of 2013 at which time all monitoring devices will be retrieved and data will be analyzed to evaluate effects of mitigation measures and help improve future management strategies.