Genetic signatures coupled with lineage shift characterise endemic evolution of Dengue virus serotype 2 during 2015 outbreak in Delhi, India.

OBJECTIVE: In 2015, New Delhi witnessed a massive outbreak of Dengue virus (DENV) resulting in high morbidity and mortality. We report the molecular characterisation of the dominant circulating DENV strain to understand its evolution and dispersal.

MATERIALS AND METHODS: DENV infections were diagnosed by detection of IgM/NS1 antigen, and serotyping was performed by C-PrM PCR. Envelope gene was amplified, and variation(s) in envelope gene were analysed. Phylogenetic tree construction, time-based phylogeny and origin of DENV were analysed. Site-specific selection pressure of envelope gene variants was analysed.

RESULTS: Confirmed DENV infection was observed in 11.34% (32 of 282) cases, while PCR positivity for C-PrM region was observed in 54.16% (13 of 24) of NS1 antigen-positive cases. All samples belonged to serotype 2 and cosmopolitan genotype. Phylogenetic analysis using envelope gene revealed segregation of cosmopolitan genotype strains into specific lineages. The Indian strains clustered separately forming a distinct monophyletic lineage (lineage III) with a signature amino acid substitution viz., I162V and R288K. Selection pressure analysis revealed that 215D, 288R and 304K were positively selected sites. The rate of nucleotide substitution was 6.93 × 10-4 substitutions site-1 year-1 with time to most common ancestor was around 10 years with JX475906 (Hyderabad strain) and JN030345 (Singapore strain) as its most probable ancestor.

CONCLUSION: We observed evolution of a distinct lineage of DENV-2 strains on the Indian subcontinent with possible changes in endemic circulating dengue strains that might give rise to more pathogenic strains.