The m strain of an attenuated Japanese encephalitis virus was found not to be infective to the mosquito, Culex tritaeniorhynchus summorosus. Various passages of the virus in hosts including mosquitoes did not essentially modify the non-infective nature of the virus to the mosquito. Neither the intraperitoneal virulence to adult mice nor the optimum pH of hemagglutinin of m strain were markedly altered during the passages, always differing from that of representative epidemic strains, parent Mukai and JaGAr # 01.
These findings suggested that the m strain possessed characters rendering it eligible as a candidate for live attenuated vaccine for swine, which are known to be the most important amplifier of Japanese encephalitis virus in nature.