Surveillance of Japanese encephalitis virus infection in mosquitoes in Vietnam from 2006 to 2008

Abstract

Japanese encephalitis virus (JEV) infection in mosquitoes was monitored in Vietnam from 2006 to 2008. A total of 15,225 mosquitoes, identified as 26 species in five genera were collected and 12,621 were grouped into 447 pools for examination of JEV infection by assays for cytopathic effects in C6/36 cells and by RT-PCR to detect flavivirus RNA. Three JEV strains were isolated from Culex tritaeniorhynchus Giles collected in northern and southern Vietnam and two JEV strains were isolated from Culex vishnui Theobald collected in the highlands of Vietnam. Genetic and phylogenetic analyses, based on complete E gene nucleotide sequences, revealed that the five JEV strains were classified into the genotype I group and six amino acid differences were found in these five strains. These results indicated that multiple JEV genotype I populations are circulating countrywide in Vietnam, transmitted by bites of their Cx. tritaeniorhynchus and Cx. vishnui.

Figure 1.

Map of Vietnam showing locations of the 11 mosquito collection sites in this study.

Figure 2.

Distribution of the eight species of Culex mosquitoes collected in four provinces in the highlands of Vietnam in June and July 2007. The “other Culex species” group contains three species: Cx. bitaeniorhynchus, Cx. quinquefasciatus and Cx. pseudovishnui.

Figure 3.

Neighbor-joining dendrogram showing phylogenetic relationships of the nucleotide sequences of the E gene of 47 JEV strains. Bootstrap values correspond to 1,000 replications. Bar denotes the nucleotide similarity distance. The shaded area marks JEV genotype I strains. GenBank accession numbers for sequences used in the phylogenetic analysis are in Table 2. The five JEV strains isolated in this study (VNHT/05/2006, VNHT/07/2006, VNKT/479/2007, VNKT/486/2007, and VNTN/04/2008) are in bold.