Electron Micrography of the Eastern Strain Equine Encephalomyelitis Virus

Abstract

In recent reports from this laboratory, there have been described the results of preliminary studies with the electron microscope on two small animal viruses, namely, the agent of rabbit papillomatosis and that of the Western strain equine encephalomyelitis. The present paper is concerned with the findings in a similar examination of the Eastern strain equine encephalomyelitis virus. “The virus was propagated in chick embryos and purified by ultracentrifugation as previously described.” The final product was dissolved in Ringer solution pH 8.5. Examinations have been made of the virus obtained from 5 different batches of diseased embryos at various intervals after purification. The dried films for electron micrography were prepared as previously described., A micrograph of the Eastern strain equine encephalomyelitis virus is shown in Fig. 1. For preparation of the film a solution containing 2.2 mg virus per cc in Ringer fluid was diluted fourfold with distilled water. As shown, the predominant images are circular in shape and appear as individuals or small irregular agglomerates dispersed at random over the field. There is present also a small amount of ill-defined amorphous extraneous material. The circular images are, like those of the papilloma and Western strain viruses, uniform in size, shape and appearance.appearance. The central dark area of the images indicates, through greater scattering of electrons, a relatively high density of the corresponding region of the virus particle. Extending peripherally from the central area, the enveloping substance appears to be progressively less dense and finally fades indefinitely into the film background. This appearance of the generality of the images gives the impression to be expected of a spherical particle made up of a loose structure of regularly arranged diffraction centers, the density in the thickest dimension diminishing toward the outer limits.