Evidence of frequent introductions of Japanese encephalitis virus from south-east Asia and continental east Asia to Japan

Abstract

The Japanese encephalitis virus (JEV) circulating in Japan consists of viruses with multiple phylogenetic origins. Phylogenetic analysis revealed that some JEV strains have recently migrated from south-east and continental east Asian countries. One phylogenetic subcluster of the JEV strains circulating in Japan was closely related to viruses isolated in Vietnam and China's inland region while other JEV subclusters were related to viruses isolated in Shanghai, China. One virus subcluster, however, was isolated solely in Japan and was not found in any other Asian country. Therefore, our data suggests that the JEVs that have remained or are circulating in Japan include a mixture of viruses that have previously migrated from south-east and continental east Asian countries.

Full Genome Sequence and Virulence Analyses of the Recent Equine Isolate of Japanese Encephalitis Virus

“…JEV/eq/Tottori/2003 was located in the branch that included strains XJ69, SH17M-2007 and XJP613 within the genotype I group. Since SH17M-2007 was isolated in Shanghai [25], and XJ69 and XJP613 were isolated in Zhejiang Province next to Shanghai city (information can be found from the databases: GenBank accession numbers EU258742 and EU090705 for XJ69 and XJP613, respectively), the result from the full length sequences suggests that JEV-transmission/introduction occurred between east China and west Japan, reinforcing a previously reported hypothesis from an E gene sequence analysis that some Japanese JEV strains (subcluster II of genotype I including Nagasaki and equine/Tottori isolates) migrated from east China [11].…”

Continuity and Change of Japanese Encephalitis Virus in Toyama Prefecture, Japan

“…This result also supports the theory that JEV was introduced from southeast Asia and continental eastern Asia to Japan. 13 Furthermore, strains of genotype III isolated before 1990 in Japan were similar to those in South Korea and Taiwan. All strains isolated in South Korea after 1991 belonged to genotype I, as did those in Japan.…”

“…Japanese encephalitis virus in Japan is considered to be a mixture of the overwintering type and a type from overseas because one subcluster was isolated only in Japan, and another type of JEV was also isolated elsewhere, such as in China and Vietnam. 13 Japanese encephalitis virus has not been isolated from overwintering mosquitoes in Japan, and JEV was shown to overwinter locally in Hokkaido, Japan because outbreaks of abortion in pigs caused by JEV were observed in early June, the interepidemic period of JEV. 20 In another report, JEV was maintained during winter in lizards experimentally, although it was not isolated from wild ones.…”

“…12,13 It has also been considered necessary to clarify how JEV strains were maintained in local areas after the most frequently isolated genotype changed from III to I in the 1990s 14 in Japan. A previous study of genetic change and variation in JEV genotype III in Taiwan 15 suggested that JEV isolates fall into three clusters by area and are genetically stable in Taiwan.…”

Trials for Risk Assessment of Japanese Encephalitis Based on Serologic Surveys of Wild Animals

“…However, no migrant breeder tested negative for the JEV antibody in this study. Nabeshima et al (2009) described that JEV is frequently introduced into Japan from Southeast Asia and continental east Asia, based on a molecular epidemiologic study and chronological order. Okinawan genotype 1 strains are closely related to strains from other parts of Japan, Korea and China, but different from Australian strains (Saito et al, 2007).…”