COMPARATIVE STUDIES ON THE STRUCTURE AND PROPERTIES OF TWO SELECTED STRAINS OF JAPANESE ENCEPHALITIS VIRUS

Abstract

Two representative strains of Japanese encephalitis virus known to differ in the mouse pathogenicity, Nakayama-Yoken and JaTH-160, were investigated in more details for biological and biochemical properties as well as for morphology as seen under the electron microscope, using purified virus materials, and compared with each other to find out difference (s) which might account for the low and high pathogenicities for mice of these two strains. The results so far obtained indicate that the former strain possessing a low pathogenicity, as determined by the peripheral route infection, is covered with a rough surface envelope, on which are placed cylindrical and spike-like subunits 7-8mμ long with a central hollow in a radially manner; it showed an optimum pH 6.2-6.4 in hemagglutinin activity, and was more stable in the HA activity and infectivity than the latter. In contrast, the latter strain possessing a high pathogenicity has been found to be covered with a smooth envelope 6-8mμ thick; it showed an optimum pH of 6.6-6.8 in the HA activity, was less heat-stable in HA activity and infectivity and had a high ratio of CF titer/HA titer. Furthermore, a marked difference in the content of C₂₄ long-chain fatty acid was found in a lipid fraction of the latter strain, as compared with low contents thereof in Nakayama-Yoken strain. Serine, glycine and threonine contained in JaTH-160 was detected in higher amounts than in Nakayama-Yoken strain. However, contents of phenylalanine, lysine and histidine were very high in the latter strain. The buoyant density of Nakayama-Yoken strain was determined to be 1.34-1.35gm/cm³ in CsCl solution, while it was 1.30-1.31gm/cm³ with JaTH-160 strain. Those differences mentioned above between the two strains are discussed in relation to their different pathogenicities for mice as tested by the neural and extraneural routes.