Diversity in the neuropathology of scrapie-like diseases in animals.

The main diagnostic histology in the spongiform encephalopathies consists of a degenerative and usually symmetrical vacuolation of neurons and a spongiform lesion in the neuropil. Sometimes there can be asymmetry. This pathology is usually confined to grey matter, but an additional white matter vacuolation is sometimes typical. The degeneration can progress to neuronal necrosis, with reactive glial changes. Photoreceptor loss in the retina occurs in some experimental models. Cerebral amyloidosis is conspicuous in many types of scrapie-like pathology in animals, but is sometimes not recognised or may be absent. Abnormal immunolabelling with anti-PrP is always associated with both the degenerative and amyloid lesion and precedes the occurrence of the degeneration in experimental scrapie models. All aspects of the pathology are closely controlled by host genetic factors and by the strain of the infecting, causal agent.