The pathogenesis of the brain lesions associated with naturally occurring and experimental canine distemper. : A study utilizing bright light, immunofluorescence and electron microscopy

The pathogenesis of the brain lesions which accompany distemper encephalitis was studied in both naturally and experimentally infected dogs. This was done by ultrastructural evaluation of the brain lesions with support by light and immunofluorescence microscopy. The naturally occurring disease was studied in 19 dogs, 16 of which had light microscopic brain lesions. All dogs examined were categorized according to the appearance of these lesions which ranged from mild microgliosis of the white matter to prominent demyelination, perivascular cuffing and cellular infiltration of the neuropil. The different categories represented the sequential development of the lesions as they appeared light microscopically and provided the basis for further extensive immunofluorescence and ultrastructural studies. The experimental disease was studied in 15 dogs inoculated intracerebrally with an attenuated distemper virus. Dogs were killed at intervals ranging from 2 days to 159 days post inoculation. Clinical signs of infection included fever, depression, and grand mal seizures. Light microscopic brain lesions included marked microgliosis, perivascular cuffing and mild status spongiosus. Definite demyelination was not apparent light microscopically although early ultrastructural lesions including mild demyelination and occasional phagocytosis of myelin were similar to those detected in naturally infected dogs