Phylogenetic analyses of DENV-3 isolated from field-caught mosquitoes in Thailand.

Dengue virus serotype 3 (DENV-3) can cause all forms of dengue diseases and is a predominant serotype in many countries. This serotype is classified into five genotypes: I-V. Genotypes I-III have widely spread throughout the world, whereas genotypes IV and V are rare. Despite the impact on the spread of dengue diseases, only a few studies have reported the characteristics of DENV present in mosquito vectors. Hence, this study aimed to identify DENV-3 genotypes and reveal genetic variation of this virus presented in field-caught mosquitoes collected from endemic areas in Thailand during 2011-2015. First, we examined the effectiveness of the E gene sequence on DENV-3 genotyping, with results supporting the use of this gene for genotype identification. Then, we sequenced this gene in ten DENV-3 strains isolated from mosquitoes. The results showed that eight and two samples were genotypes III and V, respectively, and that they are closely related to DENV-3 isolated from Southeast and East Asian samples. The translated E gene sequences showed 25 unique amino acid (AA) residues located at 23 positions. Eight out of 25 residues have different chemical properties compared to the conserved AAs that are distributed across the three domains functioning in virus-host interaction. Hence, our study reports the first DENV-3 genotype V in Thailand, with these viruses potentially influencing both the disease severity and epidemic potential of DENV-3.