EXPLANATION OF PATHOGENESIS OF JAPANESE B ENCEPHALITIS AND ESTABLISHMENT OF AVIRULENT STRAINS OF JAPANESE B ENCEPHALITIS VIRUS

Strains of JBE virus were isolated from mosquitoes and from human autopsied brain materials. Hamster kidney HK cells were selected as a host for the former strain to maintain a hypothetical pantropic nature and intraperitonealbrain passages were performed for the latter to maintain or to exaggerate more neurotropic nature of virus particles. Efforts were made to pick up less virulent virus mutant to adult mouse brain. One day eggs and HK cells were adopted as the hosts to select less virulent mutants from partially attenuated TOP strain of JBE virus. Eventually, a strain came into the light as highly attenuated one showing only a scanty death even when its large amount was inoculated into adult mouse brain. Such an attenuated variant appear to have resulted incidentally rather than being intentionally induced. In the meantime, strains of JBE virus of various histories were examined for virulence to the adult mouse. The attenuated strain was deviated from other laboratory-fixed strains by the decreased intracerebral virulence.