Abstract
Cultured chiken-embryo fibroblasts, infected with either the B-1 or KO strain of Newcastle disease virus, were examined by light, fluorescent and electron microscopy to investigate the morphogenesis of virus and virus-induced host cell alterations. Cytopathic effects produced by Newcastle disease virus consisted of degenerative changes in the cells, eosinophilic cytoplasmic and intranuclear inclusions, and multinucleate syncytia. The eosinophilic inclusions were thought to correspond to fluorescing foci or to aggregates of nucleocapsids demonstrable in both cytoplasm and nucleus. The nucleocapsids observed in the cytoplasm and nucleus were identical in ultrastructure and dimensions, and indistinguishable from those contained in virions. Spherical and filamentous viral particles developed at the cell surface by a budding process similar to that described with other paramyxoviruses. During the budding process, the nucleocapsids formed in the cytoplasm were incorporated into virions, whereas the significance of the intranuclear nucleocapsids in viral replication remained to be determined.
