Phylogenetic studies reveal existence of multiple lineages of a single genotype of DENV-1 (genotype III) in India during 1956-2007

Background: Dengue virus type 1 (DENV-1) have been mostly circulating silently with dominant serotypes DENV-2 and DENV-3 in India. However recent times have marked an increase in DENV-1 circulation in yearly outbreaks. Many studies have not been carried out on this virus type, leaving a lacunae pertaining to the circulating genotypes, since its earliest report in India. In the present study, we sequenced CprM gene junction of 13 DENV-1 isolated from Delhi and Gwalior (North India) between 2001-2007 and one 1956 Vellore isolate as reference. For comparison, we retrieved 11 other Indian and 70 global reference sequences from NCBI database, making sure that Indian and global isolates from all decades are available for comparative analysis. Results: The region was found to be AT rich with no insertion or deletion. Majority of the nucleotide substitutions were silent, except 3 non-conservative amino acid changes (I. T, A. T and L. S at amino acid positions 59,114 and 155 respectively) in the Indian DENV-1 sequences, sequenced in this study. Except two 1997-98 Delhi isolates, which group in genotype I; all other Indian isolates group in genotype III. All Indian genotype III DENV-1 exhibited diversity among them, giving rise to at least 4 distinct lineages (India 1-4) showing proximity to isolates from diverse geographic locations. Conclusion: The extensive phylogenetic analysis revealed consistent existence of multiple lineages of DENV-1 genotype III during the last 5 decades in India.