Two hidden taxa in the Japanese encephalitis vector mosquito, Culex tritaeniorhynchus, and the potential for long-distance migration from overseas to Japan.

The Culex vishnui subgroups, particularly Culex tritaeniorhynchus, are considered the primary vectors of the Japanese encephalitis virus (JEV) in Asia. Recent molecular phylogenetic analyses of JEV isolates from Asian countries have shown that JEVs with diverse genetic variants are present in Asia. Furthermore, some JEV strains have been found to have crossed the East China Sea and been introduced into Japan. In this study, the possibility of overseas migration of the JE vector mosquito, Cx. tritaeniorhynchus was examined from the genetic, physical, and meteorological perspectives. Molecular phylogenetic analysis was performed based on both whole coding sequences and on the barcoding region of the mitochondrial cytochrome c oxidase subunit I (COI) gene of Cx. vishnui subgroups collected from Asian countries. Culex tritaeniorhymchus was classified into two genetically independent taxa by COI sequences: the Japanese type (Ct-J), which inhabits Japan except for the Amami Islands of southern Japan, and the continental type (Ct-C), which inhabits the Asian region except for Japan. It was confirmed that approximately 10% of Cx. tritaeniorhynchus trapped during the summer in western Kyushu were Ct-C, and that they could fly for up to 38 h continuously. The meteorological analysis also confirmed that the atmospheric flow occurring over the continent coincided with the date of Ct-C capture. This is the first report showing the existence of two taxa in Cx. tritaeniorhynchus. Their physical and physiological characteristics suggest the possibility of long-distance migration from overseas regions to Japan across the East China Sea. Future efforts are expected to provide evidence to support the occurrence of long-distance migration of Cx. tritaeniorhynchus with JEV.

[A high school measles outbreak--control measures and vaccine efficacy].

Epidemiological investigation of a March 2007 detected measles outbreak of 28 cases in a 792-student high school in Tokyo. Students with a vaccination history had significantly milder symptoms than those without, and no cases occurred among students having two of measles vaccine in two doses of measles vaccine in their childhood. Vaccine efficacy (VE) calculated in our investigation was 93.9% (95% CI:87-97), and no significant difference was observed in vaccine type or manufacturer product. Students and parents were extremely difficult to persuade to cooperate in control measures such as emergency vaccination and home isolation through notification letters even during outbreaks. Schools should thus develop measles outbreak preparedness and response plans and identify potentially susceptible students in advance through documented proof of case histories and MCV vaccination. Outbreaks should promote early detection of patients and emergency vaccination targetting potentially susceptible students backed through close cooperation with medical facilities, education institutions, and the public health sector, together with school closures as appropriate.