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EFFICACY OF ANTEMORTEM RECTAL BIOPSIES TO DIAGNOSE AND ESTIMATE PREVALENCE OF CHRONIC WASTING DISEASE IN FREE-RANGING COW ELK (C

Posted Apr 09 2013 11:52am
EFFICACY OF ANTEMORTEM RECTAL BIOPSIES TO DIAGNOSE AND ESTIMATE PREVALENCE OF CHRONIC WASTING DISEASE IN FREE-RANGING COW ELK (CERVUS ELAPHUS NELSONI)



Ryan J. Monello1,6, Jenny G. Powers1, N. Thompson Hobbs2, Terry R. Spraker3, Katherine I. O’Rourke4,5 and Margaret A. Wild1



+ Author Affiliations



1National Park Service, Biological Resource Management Division, 1201 Oak Ridge Drive, Suite 200, Fort Collins, Colorado 80525, USA



2Natural Resource Ecology Laboratory and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, Colorado 80523, USA



3Colorado State Diagnostic Laboratory, College of Veterinary Medicine, Colorado State University, Fort Collins, Colorado 80523, USA



4United States Department of Agriculture, Agricultural Research Service, Animal Disease Research Unit, 3003 Animal Disease Biotechnology Facility, Washington State University, Pullman, Washington 99164, USA



↵6 Corresponding author (email: Ryan_Monello@nps.gov )




Abstract




A reliable antemortem test is needed to understand the ecology of chronic wasting disease (CWD) in elk (Cervus elaphus nelsoni). We measured the ability of antemortem biopsy samples from the rectal mucosa to detect the abnormal prion protein associated with CWD (PrPCWD), the relationship between test results from the obex and rectal biopsies at varying stages of CWD progression, and the prevalence of CWD in free-ranging elk from Rocky Mountain National Park, Colorado, USA. We sampled and placed radio collars on 136 adult female elk in the winter of 2007–08. Elk with biopsy samples found positive for PrPCWD by immunohistochemistry (IHC) were euthanized and the obex and retropharyngeal lymph nodes were examined with IHC. We resampled, euthanized, and necropsied 20, 25, and 34 of the remaining study elk in each of the three following winters, respectively. Sensitivity of rectal biopsy samples increased in an asymptotic fashion with follicle count and was maximized at 85% (95% credible limits [CL]=60, 98) in the beginning of the study, when a greater proportion of elk were in a detectable stage of prion infection. However, maximum sensitivity was reduced to 72% (CL=46, 94) when we included resampled elk, which included recently infected elk that were initially negative using rectal biopsies and IHC. Test results were similar between rectal biopsies and the obex, but the earliest stages of prion infection were only detected by using retropharyngeal lymph nodes. Minimum CWD prevalence was estimated to be 9.9% (CL=5.7, 15.7) using rectal biopsies, but this rose to 12.9% (CL=8.0, 19.1) when we included four elk that were likely misdiagnosed at initial capture. Our results indicate rectal biopsies can provide a useful research tool for CWD in elk populations, but should be used with caution because they can miss individuals in early stages of infection and underestimate prevalence. Prevalence estimates from this population are the highest reported to date in elk and indicate that under appropriate conditions, CWD may be able to affect the dynamics of high-density elk populations.




Biopsy Cervus elaphus chronic wasting disease Colorado CWD elk prion rectal mucosa



Received December 22, 2011. Accepted October 9, 2012.




© Wildlife Disease Association 2013








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