Histopathological and enzyme histochemical changes in experimental Semliki Forest virus infection in mice and their relevance to scrapie.

Abstract The progressive histopathology and histochemical changes in mice infected experimentally with an avirulent strain (A774) of Semliki forest virus were compared with reactions caused by a virulent strain (L10) of the same virus and with results in previous work on scrapie, cuprizone-induced encephalopahyy and viral encephalitides. Apart from cellular degeneration and infiltration, the avirulent strain of virus was characterized pathologically by focal spongiform lesions that had an irregular distribution in brain and spinal cord. These focal lesions incorporated peripheral astrocytic hypertrophy and were associated with intense activity of glycoside hydrolases, especially N -acetyl-β- d -glucosaminidase which corroborated previous biochemical results and in addition elucidated the location of enzyme changes. The nature of the lesions and their pathogenesis suggested that infection by avirulent (A774) Semliki forest virus merits a pathological classification intermediate between acute inflammatory-type encephalitis and the scrapiecuprizone type of spongiform encephalopathy.