Location: Animal Disease ResearchTitle: Efficacy of antemortem rectal biopsies to diagnose and estimate prevalence of chronic wasting disease in free-ranging elk (Cervus elaphus nelsoni)) Author
Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2012
Publication Date: 4/1/2013
Publication URL: http://handle.nal.usda.gov/10113/56642
Citation: Monello, R., Powers, J.G., Hobbs, N.T., Spraker, T.R., O'Rourke, K., Wild, M.A. 2013. Efficacy of antemortem rectal biopsies to diagnose and estimate prevalence of chronic wasting disease in free-ranging elk (Cervus elaphus nelsoni). Journal of Wildlife Diseases. DOI: 10.7589/WD.2011-12-362. Interpretive Summary: Chronic wasting disease CWD is a fatal degenerative brain disorder of deer and elk in limited areas of the United States and Canada. The disease is diagnosed in hunter-harvested or captive animals by postmortem examination of brain and lymph nodes. Diagnosis of the disease in live animals is needed to monitor disease prevalence in herds maintained in national parks, where collection of tissues from hunter-harvested animals is not possible. The lymph nodes of Rocky Mountain elk infected with CWD are characterized by the protein disease marker PrP-CWD. In this study, live elk were sedated for collection of small amounts of tissue from the rectal mucosa, a method approved for diagnosis of the related disease in sheep. After sampling, elk were fitted with radiocollars and returned to their habitat. Animals were examined over the following 3 years of the study and the results of the live animal test were compared to results from the eventual necropsy results. The ability of the live animal test to identify infected animals was 47% to 74%, showing improved accuracy with larger samples. The findings indicate that the live animal test is useful in examining some aspects of disease prevalence in infected herds, although it is not suitable for diagnosing disease in individual animals.
Technical Abstract: Chronic wasting disease (CWD) is the naturally occurring transmissible spongiform encephalopathy (TSE) of captive and free ranging cervid ruminants. Rocky Mountain elk (Cervus elaphus nelsoni) are a free-ranging species of large cervid with a habitat that includes large US national parks. Minimally invasive methods for diagnosing chronic wasting disease are needed for development of management plans appropriate for these regions. Biopsy of peripheral lymphoid tissue is a generally recognized preclinical test for TSEs in ruminants. In particular, lymphoid tissue from the recto-anal mucosal tissue provides suitable material for immunohistochemistry detection of the disease associated protein marker PrP-CWD. In this study, rectal biopsy tissue was collected from 136 adult female elk in the Rocky Mountain National Park. Elk with biopsies with evidence of PrP-CWD were euthanized and postmortem tissues examined for a definitive diagnosis. Remaining elk were monitored weekly via radiocollar transmissions. Postmortem samples were collected from elk that died during the study and 20-34 study elk were resampled, euthanized and examined postmortem during each year of the 3 year study. Specificity of the rectal biopsy when compared to the gold standard postmortem testing was 100%, while sensitivity ranged from 47% when one lymphoid follicle was present in the biopsy specimen to 74% when five or more follicles were present. For elk with presumably very early disease, PrP-CWD could be detected in the retropharyngeal lymph node at postmortem examination but not in the brain or rectal tissue. The findings indicate that antemortem biopsies may be useful in monitoring CWD in herds with disease, although individual test results may fail to detect elk in very early disease.