The more virulent genotypes of the dengue virus — GIII of DENV-3 and GI of DENV-4 — which show higher dissemination potential, evolved and dispersed in India and Sri Lanka, according to new research1.
The researchers from National Institute of Virology, Pune, looking at the history of strains circulating in the subcontinent, have also identified a new DENV-3 lineage and a new DENV-4 genotype.
Between 1960-80, all four serotyopes — DENV-1, DENV-2, DENV-3 and DENV-4 — circulated in India. Yet the dengue disease profile was mild. However, disease severity got higher after 1980 along with reported changes in the population of DENV-1 and 2.
The researchers tried to determine the population dynamics of the more virulent versions DENV-3 and 4 by sequencing the envelope (E) gene from 16 Indian isolates of DENV-3 and 11 of DENV-4. These were analyzed together with 97 DENV-3 and 43 DENV-4 global sequences. The researchers found that all Indian DENV-3 isolates belonged to genotype III, lineages C, D, E and F. The Lineage F was newly identified and represented non-circulating viruses. For DENV-4, the current viruses were found to be from genotype I, lineage C, while isolates from 1960s formed the new genotype V.
The researchers found a 1979 Indian isolate of DENV-4 to be an inter-genotypic recombinant formed out of the 1978 Sri Lankan isolate of genotype I and a 1961 Indian isolate of genotype V.
Phylogeographical analysis revealed that DENV-3 GIII viruses emerged from India and evolved through Sri Lanka while DENV-4 emerged and dispersed from India.
