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Preliminary Observations on the Experimental Transmission of Scrapie to Elk (Cervus elaphus nelsoni) by Intracerebral Inoculation

Abstract

To determine the transmissibility of scrapie to Rocky Mountain elk (Cervus elaphus nelsoni), six elk calves were inoculated intracerebrally with brain suspension from sheep naturally affected with scrapie. One elk developed a brain abscess and was euthanatized at 7 weeks postinoculation (PI), and two others died at 6 and 15 months PI because of physical injuries. At 25 and 35 months PI, two other elk died after brief terminal neurologic episodes. Necropsy of these revealed moderate weight loss but no other gross lesions. Microscopically, characteristic lesions of spongiform encephalopathy were seen throughout the brains and the spinal cords, and in both cases these tissues were positive for PrP^res by immunohistochemistry. Brains of both animals were positive for PrP^res by western blot and for scrapie-associated fibrils (SAFs) by negative stain electron microscopy. PrP^res and SAFs were not detected in the three elk that died or were euthanatized because of coincidental causes. Over 3.5 years after initiation of this experiment, the one remaining inoculated elk and two uninoculated (control) elk are alive and apparently healthy. These preliminary findings demonstrate that 1) sheep scrapie agent can be transmitted to elk by intracerebral inoculation; 2) the infection can result in severe, widely distributed spongiform change and accumulations of PrP^res in the central nervous system (CNS); and 3) based on the examination of a limited number of CNS sections from two cases, this condition cannot be distinguished from chronic wasting disease with currently available diagnostic techniques.

Key words: Elk (Cervus elaphus nelsoni); immunohistochemistry; intracerebral transmission; neuronal vacuolation; pathology; scrapie; spongiform encephalopathy.

Request reprints from Dr. A. N. Hamir, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, 2300 Dayton Avenue, PO Box 70, Ames, IA 50010 (USA). E-mail: ahamir{at}nadc.ars.usda.gov.

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