A highly attenuated rabies virus HEP-Flury strain reverts to virulent by single amino acid substitution to arginine at position 333 in glycoprotein.

An amino acid at position 333 in the glycoprotein of several fixed rabies virus strains is responsible for the pathogenicity in adult mice. Substitution of arginine at this position largely reduces the viral pathogenicity in adult mice. Attenuation by this single amino acid substitution has been established by using escape mutants selected by monoclonal antibodies and point-mutated virus generated by reverse-genetics. A highly attenuated HEP-Flury strain, which was selected by serial passages in cell cultures, has glutamine at this position. In this study, a point-mutated rHEP333R virus, having arginine at position 333, was generated and examined for the responsibility of this substitution in rabies pathogenicity. The rHEP333R acquired an ability to spread and propagate in mouse brain but the parental rHEP did not. The pathogenicity of rHEP333R to adult mice by intracerebral inoculation largely increased. We confirmed that an arginine at position 333 contributed to reversion of the pathogenicity in a highly attenuated HEP-Flury strain.