The ultrastructure of replicating Newcastle disease virus in the chick embryo chorioallantoic membrane

In Vitro and In Ovo Host Restriction of Aquatic Bird Bornavirus 1 in Different Avian Hosts

Aquatic bird bornavirus 1 (ABBV-1) is associated with chronic meningoencephalitis and ganglioneuritis. Although waterfowl species act as the natural host of ABBV-1, the virus has been sporadically isolated from other avian species, showing the potential for a broad host range. To evaluate the host restriction of ABBV-1, and its potential to infect commercial poultry species, we assessed the ability of ABBV-1 to replicate in cells and embryos of different avian species. ABBV-1 replication was measured using multi- and single-step growth curves in primary embryo fibroblasts of chicken, duck, and goose. Embryonated chicken and duck eggs were infected through either the yolk sac or chorioallantoic cavity, and virus replication was assessed by immunohistochemistry and RT-qPCR in embryonic tissues harvested at two time points after infection. Multi-step growth curves showed that ABBV-1 replicated and spread in goose and duck embryo fibroblasts, establishing a population of persistently infected cells, while it was unable to do so in chicken fibroblasts. Single-step growth curves showed that cells from all three species could be infected; however, persistence was only established in goose and duck fibroblasts. In ovo inoculation yielded no detectable viral replication or lesion in tissues. Data indicate that although chicken, duck, and goose embryo fibroblasts can be infected with ABBV-1, a persistent infection is more easily established in duck and goose cells. Therefore, ABBV-1 may be able to infect chickens in vivo, albeit inefficiently. Additionally, our data indicate that an in ovo model is inadequate to investigating ABBV-1 host restriction and pathogenesis.

An electron microscopic study of MDBK cells persistently infected with Newcastle disease virus

Ultrastructural examination of a line of MDBK cells persistently infected with Newcastle disease virus (MDBKpi cells) revealed the presence of cytoplasmic aggregates of both smooth and granular nucleocapsids. Only granular nucleocapsids aligned under modified areas of plasma membrane and were incorporated into virus particles. On the grounds of morphogenesis, there was no apparent explanation for the persistent, not-cytocidal nature of the infection. Both nuclear and cytoplasmic aggregates of smooth nucleocapsids were present in MDBKpi cells which had been held without subculture for between 40 and 130 days (aged MDBKpi cells). Modified areas of plasma membrane with associated alignment of nucleocapsids were not present in aged MDBKpi cells, and neither budding nor released virus particles were observed, indicating a block in virus maturation. It is suggested that the granular material coating granular nucleocapsids allows them to interact with modified areas of plasma membrane, thereby inducing virus budding. A deficiency of this material, as apparently occurs in aged MDBKpi cells, would therefore cause a block in virus maturation. The nature of this granular material is discussed, and we suggest that it consists of M protein.

Interaction of concanavalin A with the surface of virus-infected cells

Infection of untransformed cells with a wide-range of non-oncogenic enveloped viruses causes a significant increase in their susceptibility to agglutination by concanavalin A (Con A). The increased Con A agglutinability of these cells is not caused by an increase in the number of Con A sites on the cell surface but involves alteration in the surface properties of infected cells to allow redistribution of Con A receptors to form "patches" following binding of Con A to the cell surface. Similarities between Con A-mediated agglutination of normal cells infected with non-oncogenic viruses and the agglutination response to cells transformed by oncogenic viruses will be reviewed. Finally, the use of Con A as an experimental tool to modify the replication and cytopathogenicity of non-oncogenic viruses grown in mammalian cells will be presented.

Comparative cytopathology of Newcastle disease virus. Use of ferritin-labeled antibody on allantoic and intestinal epithelium

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.