The evolutionary path of dengue virus differs in several important aspects from its flavivirus cousins, though dengue retains many of the same clinical characteristics such as production of severe fever, myalgias, headache, hepatitis, encephalitis and haemorrhage. The phylogeny of the flaviviruses sheds little light on the origin of DENV because the closest relatives include mosquito-borne viruses that occur in several continents. However, as described by Vasilakis, more detailed phylogenetic studies of DENV suggest an Asian origin, where sylvatic cycles between non-human primates and Aedes mosquitoes arose. Unlike the other flaviviruses however, DENV evolved into four antigenically and phylogenetically distinct serotypes: DENV-1, DENV-2, DENV-3 and DENV-4. Subsequently, each of these four serotypes emerged independently into an endemic cycle of transmission between humans and Aedes albopictus. This endemic cycle is now both ecologically and evolutionarily separate from the sylvatic cycle. Thus, unlike other flaviviral pathogens, urban cycles of DENV can no longer be considered zoonotic.

It has been demonstrated that DENV evolves according to a molecular clock at a serotype- and genotype-specific rate, and that the transfer of DENV from a sylvatic cycle to sustained human transmission may have occurred on the order of 100 to 1500 years ago years ago, suggesting that the current global pandemic of all four serotypes of DENV appeared during the past century. The contemporary genetic diversity seen in all four dengue serotypes is related to population growth, urbanization, and mass transport of both virus and its mosquito vector. Using an analytical technique based on coalescent theory, it was demonstrated that DENV-2 and DENV-3 experienced two phases of exponential growth. In the first phase and for most of their history, the dengue viruses experienced a low rate of exponential growth. Thirty years ago, the rate of growth of DENV-2 and DENV-3 suddenly increased by a factor of between 15 and 20.

from Endy et al. in Frontiers in Dengue Virus Research

Labels: dengue, dengue virus, Sylvatic cycle