EXPERIMENTAL INOCULATION OF SHEEP SCRAPIE AND CHRONIC WASTING DISEASE AGENTS TO RACCOONS (PROCYON LOTOR)

Authors: Hamir, Amirali; Miller, Janice; Cutlip, Randall; STACK, MICK - VET LAB AGENCY, UK; CHAPLIN, MELANIE - VET LAB AGENCY, UK; JENNY, ALLEN - USDA, APHIS, NVSL, PL; WILLIAMS, ELIZABETH - UNIV OF WYOMING

Submitted to: Veterinary Record
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2002
Publication Date: 7/26/2003
Citation: Hamir, A.N., Miller, J.M., Cutlip, R.C., Stack, M.J., Chaplin, M.J., Jenny, A.L., Williams, E.S. 2003. Experimental inoculation of sheep scrapie and chronic wasting disease agents to raccoons (Procyon lotor). Veterinary Record. 153:121-123.

Interpretive Summary: To determine the transmissibility of scrapie and chronic wasting disease (CWD) agents to raccoons, 4 raccoon kits were inoculated intracerebrally with brain suspension from sheep with scrapie and 4 other kits were similarly inoculated with brain suspension from mule deer with CWD. Two uninoculated kits served as controls. In the scrapie-inoculated group, 3 animals became sick and were euthanized between 18 and 22 months after inoculation (PI). Although the fourth raccoon in this group did not show any clinical signs, it was euthanized at 24 months PI. Microscopic lesions of TSE were present in brain and spinal cord tissues of the sick raccoons. Tissues of these raccoons were positive by 2 other laboratory tests for TSE. At present, 3 years PI, all CWD-infected and control raccoons are alive and apparently healthy. These preliminary findings demonstrate that sheep scrapie can be transmitted to raccoons within 2 years and that diagnostic techniques currently used for surveillance of TSEs in livestock would also detect TSEs in raccoons. Based on these findings, it may be possible to differentiate TSE diseases (scrapie, CWD and transmissible mink encephalopathy) on incubation periods in raccoons. Development of raccoons as a laboratory model would provide researchers with a relatively simple, fast and inexpensive method for strain-typing of unknown TSEs in the United States.

Technical Abstract: Raccoons (Procyon lotor) are omnivorous and their diet may include carrion. Therefore, in the wild they may get exposed to carcasses of animals that may have transmissible spongiform encephalopathy (TSE). To determine the transmissibility of scrapie and chronic wasting disease (CWD) agents to raccoons, 4 raccoon kits were inoculated intracerebrally with brain suspension from sheep with scrapie and 4 other kits were similarly inoculated with brain suspension from mule deer with CWD. Two uninoculated kits served as controls. In the scrapie-inoculated group, 3 animals became sick and were euthanized between 18 and 22 months post inoculation (PI). Although the fourth raccoon in this group did not show any clinical signs, it was euthanized at 24 months PI. Gross lesions were not seen in the brain. Extensive microscopic lesions of spongifom encephalopathy were present in CNS tissues and protease-resistant prion protein (PrPres) was observed by immunohistochemistry in the three clinical raccoons. Similar results were obtained by Western blot for the detection of PrPres. At present, 3 years PI, all CWD-infected and control raccoons are alive and apparently healthy. These preliminary findings demonstrate that sheep scrapie can be transmitted to raccoons within two years and that diagnostic techniques currently used for surveillance of TSEs in livestock would also detect prions in raccoons. Since the incubation period in raccoons of another TSE, transmissible mink encephalopathy (TME) is under 6.5 months, it may be possible to differentiate these TSEs (scrapie, CWD, and TME) based on incubation periods in raccoons. Such a laboratory model would be relatively simple, fast and inexpensive for strain-typing of unknown TSEs in the United States.