Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2004
Publication Date: 1/1/2005
Citation: Hamir, A.N., Kunkle, R.A., Richt, J.A., Miller, J.M., Cutlip, R.C., Jenny, A.L. 2005. Experimental transmission of sheep scrapie by intracerebral and oral routes to genetically susceptible Suffolk sheep in the United States. Journal of Veterinary Diagnostic Investigation. 17(1):3-9. Interpretive Summary: Scrapie is a naturally occurring fatal disease of sheep and goats. It affects nervous system of the animal. Susceptibility to the disease is dependent upon genetic makeup of the host and infectious agent. This study documents findings in Suffolk sheep affected with experimental disease. Four-month-old lambs were utilized for the study. They were administered (5 in the brain and 19 orally) scrapie-infected sheep brains. All animals that were administered the infected material directly into the brain revealed signs of scrapie and were euthanized between 13'24 months after administration. In sheep given the material orally, signs of scrapie were seen between 27 and 43 months in 5 of 9 animals. Three of the 4 clinically normal sheep were found to be positive for scrapie by laboratory tests at 15, 20, and 49 months after administration of infected material. There is lack of information on experimental transmission of US scrapie agent in genetically diverse flocks of sheep. This study attempts to partially fill this void by documenting findings of this disease in Suffolks. Since similar investigations are also needed for other breeds of sheep in this country, the present study will serve as a foundation to compare results of other future studies.
Technical Abstract: Scrapie is a naturally occurring fatal neurodegenerative disease of sheep and goats. Susceptibility to the disease is partly dependent upon genetic makeup of the host. This study documents clinicopathological findings and distribution in tissues of abnormal prion proteins (PrPres) by immunohistochemical (IHC) and Western blot (WB) techniques, in tissues of genetically susceptible sheep inoculated with US sheep scrapie agent. Four-month-old Suffolk lambs (QQ or HQ at codon 171) were utilized for the study. They were inoculated (5 intracerebrally and 19 orally) with an inoculum (No. 13-7) consisting of a pool of scrapie-infected sheep brains. Intracerebrally inoculated animals were euthanized when advanced clinical signs of scrapie were observed. Orally inoculated animals were euthanized at pre-determined time-points (4, 9, 12, 15 and 21 months post inoculation, PI) and thereafter when the animals had terminal signs of disease. A detailed postmortem examination was conducted on each carcass and tissues were examined for microscopic lesions and for the presence of PrPres by IHC and WB techniques. All intracerebrally inoculated animals exhibited clinical signs of scrapie and were euthanized between 13 ' 24 months PI. Spongiform lesions in the brains and PrPres deposits in central nervous system (CNS) and lymphoid tissues were seen in these sheep. In orally inoculated sheep, clinical signs of scrapie were seen between 27 and 43 months PI in 5/9 animals. The earliest detectable PrPres was observed in brainstem and lymphoid tissues of a clinically normal sheep at 15 months PI. Three of the 4 clinically normal sheep were found to be positive at 15, 20, and 49 months PI by either histopathology or the PrPres tests. This study was done to partially fill a void in information on experimental studies of US scrapie transmission (by intracerebral and oral routes) in genetically susceptible sheep.