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Dengue (DEN) is an acute mosquito borne viral disease of mankind. Off late it has become an important public health concern in Southeast Asia. Although, all the four known dengue virus serotypes (DEN-1 to 4) are reported from time to time, in the recent past, DEN-2 has emerged as the predominant type, being the causative agent of several outbreaks of dengue fever (DF) and dengue haemorrhagic fever (DHF) in India. To elucidate the true molecular epidemiology of these viruses, we have sequenced C-prM gene junction (454 nucleotides) of 11 DEN-2 viruses directly from patient serum. The C-prM gene junction was amplified initially by reverse transcription-polymerase chain reaction followed by automated DNA sequencing. These sequences provide unique information with regard to molecular epidemiology when compared to other DEN-2 sequences from diverse geographic origins. The sequence analysis revealed that most of the mutations in this region remained silent, except a few at the carboxy-terminal of the capsid. Reported phylogenetic analysis classifies DEN-2 viruses into five distinct genotypes. The Gwalior DEN-2 viruses, included in the present study were classified into genotype-IV, and were found to be most closely related to Delhi 1996 DEN-2 viruses and FJ 10/11 strains prevalent in the Fujian state of China. However, two earlier Indian isolates of DEN-2 were classified into genotype-V. The present study indicates that genotype V of DEN-2 has been replaced by genotype IV during the past decade, which continues to circulate silently in north India, and have the potential to reemerge and cause major epidemics of DF and DHF.

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To study the genetic variability and to detect evolutionary changes and movement of dengue 2 (DEN-2) strains, nucleotide sequencing of the envelope protein gene and the nonstructural protein 1 gene junction was performed for 9 isolates from the 1996 Delhi epidemic and 1 isolate from the 1967 Delhi epidemic. The epidemic strains had a divergence of 10%-11% from the 1967 strains, but were quite similar to DEN-2 isolates from Seychelles, Somalia, and Torres Strait. In addition, the sequence data were compared to the prototype DEN-2 strain, New Guinea C, and other published DEN-2 sequences from different parts of the world. The phylogenetic analysis by the Molecular Evolutionary Genetics Analysis program suggests that the 1996 Delhi isolates of DEN-2 were genotype IV. The 1967 isolate was similar to a 1957 isolate of DEN-2, P9-122, from India, and was classified as genotype V. This study indicates that earlier DEN-2 strains of genotype V have been replaced by genotype IV.

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