Molecular epidemiology of dengue-1 and dengue-4 viruses.

Genetic variation between geographically and temporally distinct isolates of dengue-1 (DEN-1) and dengue-4 (DEN-4) viruses was investigated. The nucleotide sequences of a fragment of the envelope protein gene encoding amino acids 28 to 87 of 35 DEN-1 isolates and 28 DEN-4 isolates were determined. Maximum nucleotide sequence variation was 6.9% and 4.9% for DEN-1 and DEN-4 viruses, respectively. Taking a divergence of 6% between the nucleotide sequences as the cut-off value, three genotype groups were defined for DEN-1 viruses, whereas only one was observed for DEN-4 viruses. Molecular analysis of isolates from the South Pacific permits the classification of the recent strains of DEN-1 (1988-1989 epidemics) into a genotype distinct from the genotype which comprises earlier strains. This observation suggests that the recent epidemics were due to the introduction of a new genotype rather than to the re-emergence of the earlier strain.