Structure and Development of Viruses Observed in the Electron Microscope

Abstract

Examination in the electron microscope of ultracentrifuged preparations of vaccinia and fowl pox viruses has shown the particles generally to be brickshaped with dimensions about 210 X 210 X 260 m/~ and 265 X 265 X 330 m/~, respectively (1).In 1942, Green, Anderson, and Smadel (2) noted that va~cinia virus appeared to have a limiting membrane and an internal structure composed of a central zone of greater density, often surrounded by four small bodies. The presence of an inner body was confirmed by Sharp e~ a2. (3). Dawson and McFarlane (4) observed that the central body resisted pepsin digestion, whereas the peripheral area became less opaque to the electron beam. They noted a limiting membrane but suggested that the satellite bodies, described by Green a 02., were artefacts. Internal structure has also been seen by others (5-7), and Peters and Nasemann (8) have illustrated and described a small, dense body located at the periphery of some viral particles, which they consider to represent developmental forms. Bang e~ 02. (9) observed a dense, central body in fowl pox virus and also noted a decrease in density at the periphery of the virus particle after treatment with pepsin.Although vaccinia (10, 11) and fowl pox (12) viruses have previously been identified in sectioned tissues, the relatively thick sections employed and the distortion produced by removal of the embedding plastic with solvents have tended to obscure details of viral structure. More recently, Gaylord and Melnick (13), employing thinner sections without removal of methacrylate, noted several forms of vaccinia virus, including "empty circles" and "circles filled with homogeneous material of low electron density," as well as internal structures described as granules, bars, and dumbbells.In order to obtain further information concerning the structure and development of vaccinia and fowl pox viruses, ultrathin sections of infected * This investigation was supported by grants from

An electron microscope study of molluscum contagiosum

“…3. The finely dispersed cytoplasm, called the cytoplasmic cloud for convenience, shows the appearance of partial viral membranes at its periphery, a mode of virus development previously illustrated by Morgan et al (1954b). The mitochondria are greatly swollen and tend to be arranged around the periphery of an area of cytoplasm (u.c.)…”

“…8D. Here is shown a well delineated, denser, nucleus-like region, or nucleoid (Morgan et al 1954b), which soon becomes silhouetted from the rest of the viroplasm by a clearer region (P1. 5, fig.…”

“…7A, and shows a number of stages of virus development. Stage 1, marked on the figure, shows the first certain appearance of the virus, emerging from the general background of cell cytoplasm as a 'ghost' of viroplasm (Morgan et al 1954b). Similar stages taken from another section are shown enlarged in P1.…”

“…Stage 5 shows the continued density increase of the central viroplasm, and stage 6 the splitting of the outer membrane (Morgan et al 1954b) to form a double membrane.…”

“…The present paper is intended to show more fully the development stages of the molluscum contagiosum virus, and to compare them with those of the vaccinia and fowl pox viruses as described by Morgan et al (1954b), to which they are very similar. The accompanying changes of the epidermal cells, leading to the formation of the molluscum body, will also be shown.…”