Observations on the replication of virus and stability of virulence in Culex tritaeniorhynchus after intrathoracically inoculation with attenuated Japanese encephalitis virus SA14-14-2 vaccine strain

To investigate the replication of Japanese encephalitis(JE) SA14-14-2 vaccine virus intrathoracically inoculated to Culex tritaeniorhynchus mosquitoes and to determine its stability of viral virulence in sucking mice in order to evaluate the safety of this vaccine,the laboratory colony of C.tritaeniorhynchus was set up and the JE SA14-14-2 vaccine virus,Nak and SA14 strain virus were inoculated intrathoracically.The virus titers in the inoculated mosquitoes were determined by plaque assay after different days of infecton.and the pathogenicity to sucking mice was observed by inoculation of the infected mosquito suspensions to sucking mice or by direct biting to sucking mice with the infected mosquitoes.It was found that all these 3 strains of viruses could be detected in C.tritaeniorhynchus by plaque assay within 2-20 days in which the virus titer of SA14-14-2 was lower(2.0-3.72 log) than those of its parent strain SA14(3.0-4.85 log) and the wild strain of JE Nak virus(3.0-5.40 log) Neither illness nor death of mice could be found not only in mice inoculated with infected mosquito suspensions but also in mice directly bitten by the infected mosquitoes.These results indicate that,after intrathoracical infection,the attenuated JE SA14-14-2 vaccine strain still remains its attenuated character when the viruses replicate in mosquitoes,suggesting that no transmission of viruses can be induced when the attenuated vaccine strain of virus replicates in mosquitoes.