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

Isolation and partial characterization of a novel paramyxovirus from the gills of diseased seawater-reared Atlantic salmon (Salmo salar L)

A formerly undescribed virus has been isolated from the gills of farmed Atlantic salmon post-smolts in Norway suffering from gill disease. Cytopathic effects appeared in RTgill-W1 cells 9 weeks post-inoculation with gill tissue material. Virus production continued for an extended period thereafter. Light and electron microscopic examination revealed inclusions and replication in the cytoplasm. The viral nucleocapsid consisted of approximately 17 nm thick filaments in a herringbone pattern. Certain areas of the plasma membrane were thickened by the alignment of nucleocapsids on the internal surface and projections of 10 nm long viral glycoprotein spikes on the external surface. Virus assembly and release was achieved by budding through the modified plasma membrane. Negatively stained virions were spherical and partly pleomorphic with a diameter of 150-300 nm as seen by electron microscopy. The virus was sensitive to chloroform, heat and low and high pH, and replication was not inhibited by Br-dU or IdU indicating an RNA genome. Both haemagglutination and receptor-destroying enzyme activity were associated with the virions and the formation of syncytia in infected cultures indicated fusion activity. The receptor-destroying enzyme was identified as neuraminidase. The virus contained five major structural polypeptides with estimated molecular masses of 70, 62, 60, 48 and 37 kDa. Its buoyant density was 1.18-1.19 g ml(-1) in CsCl gradients. From the observed properties we conclude that this new virus belongs to the Paramyxoviridae and suggest the name Atlantic salmon paramyxovirus (ASPV). Furthermore, replication occurred at 6-21 degrees C, suggesting a host range confined to cold-blooded animals.

Scanning electron microscope examination of epithelial cells infected with enveloped viruses

The apical surface structure of virus infected epithelial cells (MDBK and MDCK) was examined in the SEM. Cells were infected with related enveloped viruses (influenza, Sendai, and vesicular stomatitis) under conditions of productive, nonproductive, and persistent infections. Fewer microvilli were seen in persistent infections with Sendai virus and the standard virus infected cells appeared to be normal. Extensive morphological changes, stunting of microvilli or budding effects, were noted in productive infections with influenza virus (WSN) and a reduction in the relative number of microvilli in a nonproductive infection with the PR8 strain. Although budding occurs on the basal lateral surface of VSV infected cells, morphological alterations were evident on the apical surface unlike that seen in influenza and Sendai virus infections.

Accumulation of altered viral nucleocapsids in mumps virus--persistently infected cell cultures

Two long-term human cell cultures persistently infected with mumps virus accumulated increased amounts of morphologically altered viral nucleocapsids. Alterations involved size, heterogeneity, fine structure and shape. RNA present in intracellular nucleocapsids was predominantly of subgenomic size.