Diagnosis of preclinical and subclinical scrapie in a naturally infected sheep flock utilizing currently available postmortem diagnostic techniques

Scrapie is a naturally occurring transmissible encephalopathy of sheep and goats, Currently available methods for diagnosis are the presence of charac teristic histopathologic changes and detection of an abnormal form of prion protein (PrPres) in the brains of affected animals. This study documents p reclinical. and subclinical scrapie, in a flock of 16 sheep utilizing histo pathology, immunohistochemistry (IHC), western blot, and electron microscop y (for scrapie-associated fibrils) for confirmation of the disease. Prior t o necropsy, none of the sheep showed signs of clinical scrapie. Based on th e results of histopathology and positive PrPres tests, 3 ewes were found to have subclinical scrapie. An additional ewe, which did not have histopatho logic changes in the brain but was positive by IHC and western blot, was co nsidered a preclinical case of scrapie. None of the sheep had amyloid in th e brain stem.