Molecular typing of dengue viruses circulating in Assam, India during 2016-2017.

Abstract

The global incidence of dengue has grown dramatically in recent decades and Assam, India has witnessed several outbreaks of dengue since 2015. Although during post-monsoon months (September to December), most cases of dengue in Assam are recorded but incidence of dengue in Assam has been slowly changing from being endemic to being hyper endemic. Therefore, this study was carried out to determine the serotypes and genotypes of dengue virus prevalent in Assam during the period of 2016-2017. This is a prospective study conducted for a period of two years from 2016 to 2017. Department of Microbiology, Gauhati Medical College and Hospital (GMCH) had received a total of ~12000 and ~9000 sera sample during 2016 and 2017 respectively for confirmation of clinically suspected dengue cases. For confirmation, dengue NS1 antigen and IgM antibody ELISA tests were performed. Multiplex RT-PCR was performed for serotyping of dengue viruses and representative samples found positive in PCR were sequenced to determine the genotypes of circulating dengue virus serotypes. In the year 2016, 6157 sera samples and in 2017, 3386 sera samples were found positive in ELISA test. A total of 157 dengue positive sera samples representing 17 districts of Assam were further tested by multiplex RT-PCR for serotyping of the virus. In PCR, out of 157, 107 samples (68.15%) were found positive for the presence of dengue virus genome. Out of 107, 74 samples (69.15%) were positive for dengue virus serotype-1 (DENV-1), 32 samples (29.90%) for dengue virus serotype-2 (DENV-2) and one sample (0.93%) positive for dengue virus serotype-3 (DENV-3). Out of 107 PCR positive samples, 25 samples were sequenced to identify their genotypes. Phylogenetic analysis of sequenced dengue viruses revealed that all the seven DENV-1 strains were genotype V, 17 DENV-2 strains were genotype IV (Cosmopolitan genotype) and one DENV-3 strain was genotype III. These findings improve our knowledge of circulating dengue virus serotypes in Assam. Co-circulation of three serotypes of dengue virus highlights the need for establishment of active dengue surveillance. The genotypic data of our findings will be helpful for future dengue molecular epidemiology studies and to control the disease in the region.