Abstract
Cytopathology and virion structure were compared in tissues of chicken chorioallantois and intestine infected with four Newcastle-disease-virus (NDV) strains of differing virulence and tissue tropism. Virions of the recently isolated enterotropic Ulster and viscerotropic 219 strains did not differ structurally from established NDV strains B1 and GB. A ferritin-labeled anti-NDV globulin combined with virions of all strains. In chorioallantoic membranes, the Bl and Ulster strains replicated by budding from surface allantoic epithelial cells. The GB and 219 strains replicated throughout the membrane and produced extensive necrosis; they also had a greater tendency to replicate in and damage vascular tissues. Lesions in intestine were not seen by histologic, immunofluorescent, or ultrastructural examination in control and Bl infections. The Ulster strain replicated in epithelium of the anterior intestine; viral antigens were present chiefly in the duodenum. In contrast, GB and 219 strains replicated in the submucosa of the posterior gut and induced severe enteritis with lymphoid necrosis, vasculitis, histiocytosis, and hemorrhage.