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United States Department of Agriculture

Agricultural Research Service

Title: Transmission of Sheep Scrapie to Elk (Cervus Elaphus Nelsoni) by Intracerebral Inoculation: Final Outcome of the Experiment

Authors
item Hamir, Amirali
item Miller, Janice
item Cutlip, Randall
item Kunkle, Robert
item Jenny, Allen - NVSL/APHIS/USDA, AMES, IA
item Stack, Mick - VET LABS, WEYBRIDGE, UK
item Chaplin, Melanie - VET LABS, WEYBRIDGE, UK
item Richt, Juergen

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2003
Publication Date: July 1, 2004
Citation: Hamir, A.N., Miller, J.M., Cutlip, R.C., Kunkle, R.A., Jenny, A.L., Stack, M.J., Chaplin, M.J., Richt, J.A. 2004. Transmission of sheep scrapie to elk (Cervus elaphus nelsoni) by intracerebral inoculation: Final outcome of the experiment. Journal of Veterinary Diagnostic Investigation. 16(4):316-321.

Interpretive Summary: This is a final report of an experimental transmission of sheep scrapie agent by intracerebral inoculation to Rocky Mountain elk (Cervus elaphus nelsoni). It documents results obtained in experimental and control elk. A preliminary report of this study was published previously. During the first 2 years post inoculation (PI), 3 animals died or were euthanized because of infection or injuries unrelated to scrapie. In years 3 and 4 PI, 3 other elk died after brief terminal neurological episodes. Examination of these animals revealed moderate weight loss but no other lesions. Microscopic examination and laboratory tests of these elk confirmed infection by the scrapie agent. Lesions and tests for the scrapie agent were not detected in the 3 inoculated elk examined during the first 2 years or in the 2 control animals. These findings confirm that intracerebral inoculation of sheep scrapie agent results in positive tests and lesions for the scrapie agent in elk. Based on these findings, this condition cannot be distinguished from chronic wasting disease (CWD) of elk with currently available diagnostic techniques. Results of this study will have most impact on wildlife biologists, veterinarians, and TSE researchers who will become aware that US sheep scrapie is transmissible to elk and that microscopic lesions and laboratory tests used for the diagnosis TSEs cannot differentiate this experimental TSE from CWD of elk and other cervids.

Technical Abstract: This is a final report of an experimental transmission of sheep scrapie agent by intracerebral inoculation to Rocky Mountain elk (Cervus elaphus nelsoni). It documents results obtained in experimental (n = 6) and control (n = 2) elk. A preliminary report of this study was published previously.7 During the first 2 years post inoculation (PI), 3 animals died or were euthanized because of infection or injuries other than spongiform encephalopathy (SE). In years 3 and 4 PI, 3 other elk died after brief terminal neurological episodes. Necropsy of these animals revealed moderate weight loss but no other gross lesions. Microscopically, characteristic lesions of SE were seen throughout the brains and spinal cords, and the tissues were positive for proteinase-K resistant prion protein (PrPres) by immunohistochemistry (IHC) and by Western blot. Also, scrapie-associated fibrils (SAF) were observed by negative stain electron microscopy in the brains of elk with neurologic signs. PrPres and SAF were not detected in the 3 inoculated elk necropsied during the first 2 years or in the 2 control animals. Retrospective analysis of the gene encoding cervid PrP revealed a polymorphism at codon 132. The neurologic elk were either homozygous (MM) or heterozygous (LM). These findings confirm that intracerebral inoculation of sheep scrapie agent results in SE with accumulations of PrPres in the CNS of elk, and based on morphologic and IHC findings, this condition cannot be distinguished from chronic wasting disease (CWD) of elk with currently available diagnostic techniques.

Last Modified: 11/20/2014
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