Phylogenetic analysis reveals cocirculation genotype of all four dengue virus serotypes in Thailand.

Dengue fever is a hyperendemic disease in Thailand caused by four distinct dengue virus serotypes (DENV-1 to 4) that co-circulate annually. Fluctuating endemic patterns make it difficult to predict outbreaks in hyperendemic regions. Additionally, the envelope protein is associated with cocirculation of several serotypes, cocirculation of different strains within the same genotype, and heterotypic dengue infection. To control dengue epidemiology, phylogenetic analysis of envelope gene sequences and geographic distribution should be conducted. In this report, we characterized 305 dengue envelope genes isolated from blood samples of dengue-infected Thai patients from 1999 to 2012. Phylogenetic tree analysis of the envelope gene nucleotide sequences of 305 strains revealed that they comprised 128 strains of DENV-1, classified as genotype I; 56 strains of DENV-2, classified as Asian I and cosmopolitan genotypes; 56 strains of DENV-3, classified as genotypes I, II, and III; and 65 strains of DENV-4, classified as genotypes I and II. The results attributed DENV-1 to 4 to distinct locations in Thailand, with recurrent circulation in the original region for similar periods. In addition, DENV-1 genotype I was the main strain circulating almost annually between 1999 and 2012, whereas DENV-2 Asian I was the predominant genotype isolated between 2010 and 2012. Taken together, all four serotypes may have co-circulated in Thailand from 1999 to 2012. DENV-1 to 4 were particularly homogeneous circulating genotypes. Therefore, the molecular diversity of the dengue envelope gene has been co-circulating in Thailand for over a decade.