Molecular detection and characterization of dengue isolates circulating in north India

BACKGROUND AND OBJECTIVES: In recent decades, the incidence of dengue has increased dramatically. In dengue-endemic countries, changes in dengue virus serotypes, genotypes, and lineages have been reported. This study was designed to detect and characterize the dengue virus isolates circulating in North India by serological and molecular techniques. MATERIALS AND METHODS: This study was conducted at the Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, India. NS1 antigen and IgM antibody against dengue were detected by ELISA methods, viral RNA was extracted and amplified by conventional PCR and one-step single-tube multiplex PCR. The purified PCR products were cycle sequenced and a database search was implemented for the confirmation of the sequence product. Phylogenetic analysis was carried out with previously reported sequences. RESULTS: Among 1509 samples, 205 (13.6%) were found positive for IgM antibodies with the highest number (n=67) among the 21 to 30 years age group with peak positivity during post-monsoon months. Among acute samples, NS1 antigen was positive in 62.9%. Seven patients out of 13 had dengue viral RNA in PCR. It comprised six DENV-2 serotypes and one DENV-3 serotype. On phylogenetic analysis, DENV-2 strains grouped with genotype IV and DENV-3 with genotype III. CONCLUSION: Dengue infection was found frequently during post-monsoon season. The positivity rate of the dengue NS1 antigen test was greater than that of the antibody test. The dengue isolates were characterized as genotype IV and genotype III of DENV-2 and DENV-3 respectively.