|Stack, Mick L|
Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2002
Publication Date: N/A
Citation: Interpretive Summary: Scrapie is a naturally occurring transmissible spongiform encephalopathy (TSE) of sheep and goats. It has also been proposed as the possible origin of chronic wasting disease (CWD) of elk and deer. To test the transmissibility of sheep scrapie agent to elk, 6 elk calves were inoculated intra-cerebrally with brain suspension from scrapie infected sheep. One elk developed a brain abscess and 2 others suffered physical injuries within 15 months and were euthanized. At 25 and 35 months after infection, 2 other elk died after a brief terminal nervous signs. Examination of these carcasses revealed moderate weight loss. Microscopic lesions indicating scrapie-like lesions were seen in the brains and the spinal cords in both cases, 3 other laboratory tests were positive for scrapie-like agent. These results indicate that: 1) Elk are susceptible to sheep scrapie by intra-cerebral route of exposure; and 2) Microscopic lesions and laboratory tests cannot differentiate this type of infection from CWD. The research of this study will be used by TSE researchers and veterinarians who for the first time are going to be aware that sheep scrapie can be transmitted to elk and that microscopic lesions and laboratory tests for TSEs cannot differentiate this type of infection from CWD.
Technical Abstract: Scrapie is a fatal naturally occurring transmissible spongiform encephalopathy (TSE) of sheep and goats. To determine the transmissibility of scrapie to Rocky Mountain elk and to obtain clinico-pathological information, including detection of proteinase-resistant prion protein (PrPres), 6 elk calves were inoculated intracerebrally with brain suspension from sheep naturally affected with scrapie. One elk developed a brain abscess and was euthanized at 7 weeks post inoculation (PI) and 2 others died at 6 and 15 months PI because of coincidental physical injuries. At 25 and 35 months PI, 2 other elk died after a brief terminal neurological episodes. Necropsy of these elk revealed moderate weight loss. Characteristic microscopic lesions of spongiform encephalopathy were seen throughout the brains and the spinal cords in both cases and these tissues were positive for PrPres by immunohistochemistry. Both brains were positive efor PrPres by Western blot and for scrapie-associated fibrils (SAF) by negative stain electron microscopy. Three years after initiation of this experiment the remaining inoculated elk and two control elk are still alive and apparently healthy. These 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 PrPres and SAF in the CNS; and 3) clinicopathologically, this condition cannot be distinguished from infection caused by chronic wasting disease (CWD) agent with currently available diagnostic techniques.