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United States Department of Agriculture

Agricultural Research Service

Title: Second Passage of Sheep Scrapie and Transmissible Mink Encephalopathy (Tme) Agents in Raccoons (Procyon Lotor)

Authors
item Hamir, Amirali
item Kunkle, Robert
item Miller, Janice - ARS RETIRED
item Richt, Juergen

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2005
Publication Date: November 1, 2005
Citation: Hamir, A.N., Kunkle, R.A., Miller, J.M., Richt, J.A. 2005. Second passage of sheep scrapie and transmissible mink encephalopathy (TME) agents in raccoons (Procyon lotor). Veterinary Pathology. 42(6):844-851.

Interpretive Summary: Agents of transmissible spongiform encephalopathy (TSE) include sheep scrapie, bovine spongiform encephalopathy (mad cow disease, BSE), transmissible mink encephalopathy (TME), and chronic wasting disease (CWD). In this study 3 groups of raccoons were inoculated in the brain with either TME or scrapie (2 different sources). Two other uninoculated raccoons served as controls. All animals in the TME-inoculated group showed clinical signs of neurologic disorders and were euthanized between 6 and 8 months post inoculation (PI). Raccoons in the 2 scrapie-inoculated groups revealed similar clinical signs, but such signs were observed much later and the animals were euthanized between 12 and 18 months PI. Examinations of the carcasses revealed no gross lesions in any of the raccoons. In the inoculated animals, lesions were observed in the brain by light microscopy and the presence of disease agent was detected by 2 laboratory tests. These findings confirm that both TME and sheep scrapie are experimentally transmissible to raccoons and that the incubation periods for both agents are distinct. Therefore, it may be possible to use raccoons for differentiating unknown TSE agents. Further studies, in regards to the incubation period and the pattern of deposition of the disease agent in BSE and other isolates of scrapie, CWD, and TME in raccoons are needed before the model can be further characterized for differentiation of TSE agents.

Technical Abstract: To determine the transmissibility and pathogenicity of sheep scrapie and transmissible mink encephalopathy (TME) agents derived from raccoons (first passage), raccoon kits were inoculated intracerebrally with either TME (1 source) or scrapie (separately from 2 sources). Two uninoculated raccoon kits served as controls. All animals in the TME-inoculated group showed clinical signs of neurologic disorders and were euthanized between 6 and 8 months post inoculation (PI). Raccoons in the 2 scrapie-inoculated groups revealed similar clinical signs, but such signs were observed much later and the animals were euthanized between 12 and 18 months PI. Necropsy examinations revealed no gross lesions in any of the raccoons. Spongiform encephalopathy was observed by light microscopy and the presence of protease-resistant prion protein (PrPres) was detected by immunohistochemistry (IHC) and Western blot techniques. The IHC test revealed distinct pattern of anatomic distribution of PrPres in the TME- and scrapie-inoculated raccoons. These findings confirm that both TME and sheep scrapie are experimentally transmissible to raccoons and that the incubation periods and IHC distribution for both agents are distinct. Therefore, it may be possible to use raccoons for differentiating unknown transmissible spongiform encephalopathy agents. Further studies, in regards to the incubation period and the pattern of PrPres deposition on IHC in bovine spongiform encephalopathy (BSE) and other isolates of scrapie, chronic wasting disease (CWD), and TME in raccoons are needed before the model can be further characterized for differentiation of TSE agents.

Last Modified: 7/30/2014
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