HISTOLOGICAL CHANGES IN THE CENTRAL NERVOUS SYSTEM FOLLOWING EQUINE ENCEPHALOMYELITIS

Abstract

Histologic and cytologic study of the brain and spinal cord of the horse, guinea-pig and man subjected to the virus of equine encephalomyelitis shows characteristic features of pathologic change. The most constant of these is a perivascular infiltration, found in horses, guinea-pigs and human material affected by the virus, but not in control material. Many of the nerve cells of virus-infected material show varying degrees of degeneration of Nissl substance, many cells, especially in the brain stem and spinal cord, show various stages of necrosis, and many are in process of phagocytosis by leucocytes. Cytoplasmic inclusion bodies are present in many of the nerve cells of all material affected by the virus. Similar inclusions are found in smaller numbers in 3 horses which died from undetermined sepsis and also in a normal horse aged 12 yrs. The number of inclusion bodies in virus-infected animals is considerably greater than in the controls, and appears to be increased by the pathologic conditions of the disease. Intranuclear inclusions in the form of eosinophilic granules are also found in some of the nerve cells of horses and guinea-pigs affected by the virus, but this feature is less constant than the cytoplasmic inclusions, and the degenerative changes of the nerve cells.