Budding of fowlpox and pigeonpox viruses at the surface of infected cells

Chick embryo fibroblasts and chorioallantoic membranes infected with fowlpo x virus (FWPV) or pigeonpox virus (PPV) were examined by transmission and s canning electron microscopy. Immature virus particles were observed in fine ly granular areas, i.e. virus factories, of the cytoplasm. These particles had various forms depending on their stages of development. Many tubular st ructures were also seen in these regions. Mature virus particles with ellip soidal or brick-shaped forms enclosing electron-dense cores were detected t hroughout the cytoplasm. Notably, there was a high frequency of virus buddi ng at the cell surface, but only occasional virus wrapping in the cytoplasm . Another remarkable feature of the infected cells was accumulation of many virions just beneath the plasma membrane, indicating that this phenomenon is closely related to virus budding. Based on the observed frequency of bud ding, this mechanism seems to be the predominant way for FWPV and PPV to ex it the cell.