Intraneuronal enzymic inclusions in the histological diagnosis of scrapie

Cumulative results are presented of histopathological and enzyme histochemical findings in sheep naturally or experimentally infected with scrapie compared with healthy controls or animals with other diseases. Two hundred and sixty-eight sheep were examined, including 210 cases of clinical or suspected scrapie. According to the nature and distribution of histopathological changes, especially neuropil vacuolation and neuronal vacuoles, scrapie-affected sheep were classified into groups. In particular, examination of medulla oblongata revealed a consistently different pattern of lesions between natural scrapie (type A) and experimental scrapie (type B). Cytoplasmic enzymic inclusions demonstrated by methods for beta-glucuronidase and for acid phosphatase were regularly found in neurones from scrapie sheep but not from control animals. They appeared to be more prevalent in type B than in type A scrapie and were demonstrable even in tissue affected by post-mortem autolysis. The distribution of enzymic inclusions ranged from Betz cells of cerebral cortex to grey matter of the lumbar region of spinal cord. The detection of enzymic inclusions is a useful diagnostic criterion and has been incorporated into histological diagnostic procedures for scrapie.