Molecular epidemiology of dengue viruses

All four dengue viruses are distributed in Asia, the Americas and the Pacific islands. Emergence of dengue hemorrhagic fever (DHF) in the Pacific and the Americas is being considered a major public health problem. Studies on the molecular evolution and epidemiology of all four dengue viruses (DEN-1, DEN-2, DEN-3 and DEN-4) using genome-sequence relatedness have demonstrated the occurrence of genotype groupings among these viruses. Distinct genotypes within each virus serotype have become distributed worldwide over time and geographically. Furthermore, certain genotypes of the viruses have been associated with severe disease potential. Since the 1960s, dengue has continuously been transmitted in French Polynesia during almost four decades as successive epidemics caused generally by a different virus serotype. Apart from the overlapping circulation of both endemic virus and newly introduced virus at the beginning of the current epidemic, only one serotype was transmitted during theinterepidemic intervals. Each time, genetic analysis of the causative viruses showed that the current epidemics were due to the introduction of a genotype different from the viruses recovered from the past epidemics. Moreover, emergence of DHF in the Pacific region during the recent epidemics of DEN-3 was associated with the introduction of a new genotype from Indonesia. These observations emphasize the need for active clinical and virological surveillance to prevent and control epidemics together with molecular characterization of the viruses as part of the investigation of a dengue epidemic. At present, a new genotype of DEN-2 is bring transmitted on Tahiti.