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

Abstract

Abstract. To determine the mechanisms of maintenance and evolution of Japanese encephalitis virus (JEV) in a temperate zone, we attempted to isolate JEV from mosquitoes and pigs in Toyama Prefecture, Japan. A total of 87 JEVs were isolated from female Culex tritaeniorhynchus mosquitoes and pigs during [2005][2006][2007][2008][2009]. The prevalence of JEV in Toyama Prefecture was seasonally late in comparison with that of the virus during 1966-1972. Furthermore, JEVs were isolated after the peak in the number of female Cx. tritaeniorhynchus . Among JEV strains isolated in this study, two distinct groups were observed within genotype I of the phylogeny generated from nucleotide sequence information derived from the envelope and capsid/premembrane genes: strains belonging to the major type were isolated during 2005-2009, and strains from the minor type were isolated only in 2007. The major type has exhibited gradual change in its envelope and capsid/ premembrane genes, and all isolates obtained in 2008 and 2009 had a novel deletion of seven nucleotides in the variable region of the 3′-untranslated region.

Surveillance of Japanese Encephalitis Virus Infection in Mosquitoes in Vietnam from 2006 to 2008

“…[26][27][28][29] Single amino acid substitutions at several E protein positions have been suggested to be associated with JEV virulence. For example, a Glu to Lys substitution at amino acid 138 attenuates JEV virulence, 26,27 and a Met to Lys substitution at amino acid 279 increases JEV virulence in mice.…”

“…28 In addition, a Ser to Arg substitution at amino acid 123 affects JEV growth and pathogenicity. 29 Alignment of JEV E gene nucleotide sequences in the GenBank database showed that the great majority of JEV strains had Ser, not Arg, at residue 123. 29 The five Vietnamese JEV isolates in this study had Further data are needed to explain the function and mechanism of the E protein in JEV infection, and on other structural and non-structural JEV proteins (e.g., prM and NS4A [52][53][54] ) and on the JEV 5 and 3 NTRs.…”

“…29 Alignment of JEV E gene nucleotide sequences in the GenBank database showed that the great majority of JEV strains had Ser, not Arg, at residue 123. 29 The five Vietnamese JEV isolates in this study had Further data are needed to explain the function and mechanism of the E protein in JEV infection, and on other structural and non-structural JEV proteins (e.g., prM and NS4A [52][53][54] ) and on the JEV 5 and 3 NTRs. 29,55 This study has identified multiple JEV populations in Vietnam, and the nucleotide sequences of these JEVs were similar to those isolated in other area of Asia.…”

“…29 The five Vietnamese JEV isolates in this study had Further data are needed to explain the function and mechanism of the E protein in JEV infection, and on other structural and non-structural JEV proteins (e.g., prM and NS4A [52][53][54] ) and on the JEV 5 and 3 NTRs. 29,55 This study has identified multiple JEV populations in Vietnam, and the nucleotide sequences of these JEVs were similar to those isolated in other area of Asia. This suggested that some JEV strains have migrated between different areas in Asia by vector mosquitoes.…”

“…Therefore, in the current study, we focused on JEV infection in mosquitoes throughout Vietnam, not only in northern areas, to investigate the current distribution of JEV in Vietnam. It has recently been reported that there are amino acid variations in the E protein among JEV genotype I strains [26][27][28][29] ; we also carried out genetic and phylogenetic analyses of viral E gene sequences to study the relationships between Vietnamese JEVs and JEVs from other areas of Asia. Mosquito collection.…”