Intracellular Forms of Pox Viruses as Shown by the Electron Microscope (Vaccinia, Ectromelia, Molluscum Contagiosum)

Abstract

The intracellular development of three pox viruses has been studied with the electron microscope using thin sections of infected tissue. Cells infected with vaccinia, ectromelia, and molluscum contagiosum viruses all form developmental bodies preliminary to the production of mature virus. Developmental bodies, believed to be virus precursors, are round to oval, slightly larger than mature virus particles, less dense to electrons, and have a more varied morphology. It is suggested as a working hypothesis that the process of maturation of a virus particle takes place as follows. In the earliest form the developmental bodies appear as hollow spheres, imbedded in a very dense cytoplasmic mass constituting an inclusion body, or in a less dense matrix near the nucleus in cells without typical inclusion bodies. The spheres become filled with a homogeneous material of low electron density. A small, dense granule appears in each developmental body and grows in size at the expense of the low density material. Following growth of the granule, particles are found with the dimensions of mature virus and having complex internal structure resembling bars or dumbells. Mature virus is ovoid and very dense to electrons. An "empty" interior may be found within its thick walls.

Ontogenesis of Human Smallpox Virus

“…This period ends with the formation in the cytoplasm of large zones of dense osmiophilic material called "matrix" (1) or "viroplasm" (4), and therefore it is the final stage of this period that can be studied by electron microscopy. The distinctive feature of this period is the absence of the viral membrane around the nucleoid (14).…”

Unusual Features of Vaccinia Virus Extracellular Virion Form Neutralization Resistance Revealed in Human Antibody Responses to the Smallpox Vaccine

“…A vaccinia virus virion is a cylinder with approximate dimensions of 360-nm height by 130-nm radius (20,(81)(82)(83)(84); this gives a surface area of 400,239 nm 2 . The virion mass is 5 ϫ 10 Ϫ15 g and is 90% protein, therefore 4.5 ϫ 10 Ϫ15 g/virion.…”

Internal Structure of Rickettsia burnetii as shown by Electron Microscopy of Thin Sections

“…Animal viruses have been examined in thin sections of infected tissue. Vaccinia and fowl-pox viruses are oval with a single or double limiting membrane and an eccentrically placed inner body (Gaylord & Melnick, 1953;Morgan, Ellison, Rose & Moore 1954b); herpes virus is round or oval with a central body and one or two membranes probably depending upon the stage of development and the position in the cell (Morgan, Ellison, Rose & Moore 1954 a ) ; elementary bodies of meningo-pneumonitis virus are dense with central granules, but large circles with no internal granules are also seen in sections of infected tissue (Gaylord, 1954).…”