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United States Department of Agriculture

Agricultural Research Service

Title: Diagnosis of Preclinical and Subclinical Scrapie in a Naturally Infected Sheep Flock Utilizing Currently Available Post Mortem Diagnostic Techniques

Authors
item Hamir, Amirali
item Miller, Janice
item Schmerr, Mary Jo
item Stack, Mick - VLA, WEYBRIDGE, UK
item Chaplin, Melanie - VLA, WEYBRIDGE, UK
item Cutlip, Randall

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2000
Publication Date: N/A

Interpretive Summary: Scrapie belongs to a family of diseases which are collectively known as transmissible spongiform encephalopathies of animals and humans. It is a naturally occurring disease of sheep and goats that affects the brain. There are several currently available methods for confirmation of the disease. Most of these methods utilize brain tissue for the purpose of confirmation of the disease. In this study we used 4 different techniques for confirmation of scrapie in an infected flock of sheep. In the present study, neither the owner of the flock nor the field veterinarian noticed any abnormal nervous signs in the sheep. Also, 3 other veterinarians at NADC did not see signs compatible with brain abnormality in the sheep. However, based on the results of the tests used to confirm the disease, 3 ewes were found to have scrapie. An additional ewe, which did not have lesions in the brain but was positive by 2 other tests, was considered also opositive for the disease. Although the results of the different diagnosti tests are not directly comparable (since they were not able to test the same area of the brain), it appeared that no particular test was found to be superior or inferior at detecting scrapie in affected sheep. This study impacts on the validity of the currently used diagnostic methods for confirmation of scrapie in the United States.

Technical Abstract: Scrapie is a naturally occurring transmissible encephalopathy of sheep and goats. Currently available methods for diagnosis are the presence of characteristic histopathological changes and detection of PrP**res in the brains of affected animals. In this study we document preclinical and subclinical scrapie in a flock of sheep by utilizing histopathology, immunohistochemistry (IHC), Western blot, and electron microscopy (scrapie associated fibrils, SAF) for confirmation of the disease. Prior to necropsy none of the sheep showed signs of clinical scrapie. Based on the results of histopathology and positive PrP**res tests, 3 ewes were found to have subclinical scrapie. An additional ewe, which did not have histopathological lesions in the brain but was positive by IHC and Western blot, was considered a preclinical case of scrapie. None of the sheep revealed presence of amyloid in the brain stem.

Last Modified: 8/22/2014
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