High-voltage electron microscope study of the release of vaccinia virus from whole cells

High-voltage (1,000-kV) electron microscope examination of whole BSC-1 cells infected with vaccinia virus at different times after infection revealed the presence of increasing numbers of virions no longer confined to factories but situated along the cell periphery of monolayer cells. Stereoscopic images showed each virus enclosed within a membrane-like component of the host cell cytoplasm. Viruses within factories appeared to lack similar enclosures. Cytochalasin B, but not vinblastine, caused the enclosures to disrupt. Vaccinia viruses were observed to escape the host cell individually from the tips of microvillie and within packets of cytoplasm. Observations suggest that the intracellular movement and release of vaccinia virus utilize a host cell cytoplasmic network that involves microfilaments for stability.