It is not known with certainty when and where the progenitor of the approximately 80 species in the genus Flavivirus first arose, although geographic evidence suggests that this ancestral flavivirus may have first appeared in Africa. Over the course of speciation, the flaviviruses have shown substantial ecological diversification. Most notably, different lineages of flaviviruses adapted to different modes of transmission. A current phylogenetic tree of the genus Flavivirus shows that the basal-most lineages are viruses that have only been isolated from mosquitoes and are not known to infect vertebrates at all. This suggests that the ancestor of the genus may have been a 'mosquito-only' virus that later acquired the ability to infect vertebrates.

The remaining flaviviruses are divided into vector-borne viruses of vertebrates, with major groups using ticks and mosquitoes for horizontal transmission, and another group that infects vertebrates without the use of arthropod vectors. This topology does not suggest whether vector-borne or non-vectorborne transmission was ancestral, but the basal position of the 'mosquito-only' viruses suggests that mosquito-borne transmission among vertebrates may have preceded the loss of vector transmission. Tick-borne transmission may have evolved from a mosquito-borne lineage after the lineage that infects only vertebrates arose.

from Endy et al. in Frontiers in Dengue Virus Research

Labels: flavivirus, Mosquito-borne, Viruses of vertebrates

Positive strand RNA viruses, including flaviviruses, generally utilize the translational machinery of the host to synthesize viral proteins either in a cap-dependent or cap-independent manner to produce polyprotein precursors which are then processed into mature proteins. Polyprotein processing is accomplished by the concerted action of host and viral proteases. While some viruses, such as the hepatitis C virus code for more than one protease to perform distinct functions, flaviviruses code for a novel two-component serine protease which participates in early and late stages of the viral life cycle.

from R. Padmanabhan and Alex Y. Strongin in Frontiers in Dengue Virus Research

Further reading: Dengue Virus

Labels: dengue, dengue fever, dengue virus, flavivirus, Flaviviruses

Dengue virus (DENV), a mosquito-borne flavivirus, is the causative agent of dengue fever, currently one of the most significant emerging disease challenges to global public health. Although dengue is an old disease, recent decades have seen an unprecedented increase in the geographic range, incidence, and severity of infection. The virus infects 100 million people annually and is endemic in many tropical and sub-tropical regions in the world.

At present, neither a licensed vaccine nor anti-viral drugs are available to control dengue disease, prompting a plethora of research initiatives aimed at understanding the molecular and cellular virology, genomics, and evolution of this important virus.

Further reading: Frontiers in Dengue Virus Research

Labels: dengue, dengue disease, dengue fever, dengue virus, DENV, flavivirus