Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2007
Publication Date: 1/1/2008
Citation: Hamir, A.N., Kunkle, R.A., Richt, J.A., Miller, J.M., Greenlee, J.J. 2008. Experimental transmission of US scrapie agent by nasal, peritoneal, and conjunctival routes to genetically susceptible sheep. Veterinary Pathology. 45(1):7-11. Interpretive Summary: This study documents experimental inoculation of scrapie into genetically susceptible sheep via three different inoculation routes (nasal, peritoneal, and conjunctival). Except for two sheep, all inoculated animals were euthanized when advanced clinical signs of scrapie were observed between 19-46 months post inoculation (MPI). Lesions of scrapie were present in the brains of these sheep and the agent was detected in their tissues by laboratory tests. One intranasally inoculated sheep euthanized at 12 MPI had presence of the agent in the upper respiratory tract. These results indicate that the upper respiratory tract (specifically the pharyngeal tonsil) may serve as a portal of entry for the scrapie agent in scrapie-infected environments.
Technical Abstract: Scrapie is a naturally occurring fatal neurodegenerative disease of sheep and goats. This study documents incubation periods, pathological findings and distribution of abnormal prion proteins (PrP**Sc) by immunohistochemistry in tissues of genetically susceptible sheep inoculated with U.S. sheep scrapie agent. Four-month-old Suffolk lambs (QQ at codon 171) were inoculated by one of three different routes (nasal, peritoneal and conjunctival) with an inoculum (No. 13-7) consisting of a pool of scrapie-affected sheep brains. Except for two sheep, all inoculated animals were euthanized when advanced clinical signs of scrapie were observed between 19-46 months post inoculation (MPI). Spongiform lesions in the brains and labeling of PrP**Sc in central nervous system (CNS) and lymphoid tissues were present in these sheep. One intranasally inoculated sheep euthanized at 12 MPI had presence of PrP**Sc which was confined to the pharyngeal tonsil. These results indicate that the upper respiratory tract, specifically the pharyngeal tonsil may serve as a portal of entry for prion protein in scrapie-infected environments.