The changes in cell organelles of neurons in the brains of adult mice and hamsters during Semliki Forest virus and louping ill encephalitis.

Although Semliki Forest virus and louping ill belong to 2 distinct serological groups of arboviruses, the general pattern of cellular changes and their mode of morphogenesis is similar. Severe changes in the mitochondria of neurons, leading to the formation of inclusion bodies have been described in both infections. The possible origin of globular bodies and of the intracytoplasmic membrane convolutions from mitochondria has been suggested. In both infections virus maturation is preceded by the appearance of large accumulations of particles resembling ribosomes. Definite morphogenesis of nucleoids was traced to the cytoplasmic matrix in the close vicinity of vesicular membranes, while maturation of virions was regularly observed in the endoplasmic reticulum and occasionally within the intracytoplasmic inclusion bodies. In louping ill however, mature virus particles were seen within the vesicles of the distended and hypertrophied Golgi apparatus.