THE HISTOLOGY OF EQUINE ENCEPHALOMYELITIS

Abstract

The eastern strain of the equine encephalomyelitis virus evokes in the horse, calf, sheep, and dog an unusually intense encephalomyelitis characterized by acute primary degeneration of nerve cells, the appearance of nuclear inclusions, polymorphonuclear infiltration with early microglial proliferation, and perivascular infiltration. Lesions are more marked in cerebral cortex, thalamus, and hypothalamic regions than elsewhere; meningeal infiltration is secondary. Similar changes in horses with the western strain of virus are less intense and extensive. In small laboratory animals, such as the guinea pig, the eastern virus causes an acute encephalomyelitis especially affecting the higher olfactory centers, with nuclear inclusions in nerve cells and tiny oxyphilic bodies in glial and mesodermal nuclei. In this animal there was also a bronchopneumonia. There was no difference in type of disease produced in guinea pigs by eastern or western strains of virus.