1959 Volume 9 Issue 2 Pages 165-190
Multiplication of poxvirus in vitro including ectromelia virus, vaccinia virus and variola virus were studied using chick embryo fibroblast, strain L cells and HeLa cells as host cells.
Relationships could be established among the growth cycle of virus determined by infectivity titrations, the cellular alterations under the conventional light microscopy and the presence of virus or materials of components associated with virus within the cells seen in the electron microscope.
In growth cycle experiments no increase in the amount of cell-associated virus was observed during the first 6 hours in any of the infectious systems used. A peak virus titer was attained in 15-to 18-hour-infection. Ectromelia and variola virus adsorped on the host cells were photographed using ultrathin sectioning. Intracytoplasmic inclusions (matrix) appeared 3 hours following infection, The first recognizable viral form, so-called developmental form, were exclusively observed within the matrix area in 6-hour-infection. Most of them were limited by a double membrane. Structural appearances of the nucleoid or viroplasm in stricted area were almost the A same as those of matrix material. Coiled thread measuring about 20 to 30Å in width were seen in them. Developmental form is matured infective virus or a vegetative phase of virus from the point of view of dynamic infectivity. At later stage of infection in ectromelia-fibroblast or-L cell system another quite different intracytoplasmic inclusions appeared which did not play a necessary role in viral multiplication.
Mature forms were observed in the matrix area in a later stage of infection. The structures of them show quite characteristic appearances and it is very easy to distinct from the developing form by the presence of two kinds of double membranes, by their shape, by smaller size and by rather stronger density in thicker sections. Experiments showed that so-called mature form appearing in a later stage was resting form of virus.
