Dengue Virus Notes.
The dengue virus (DENV) in one of four serotypes and the cause of dengue fever. All four serotypes can cause the full spectrum of disease.
It is a mosquito-borne, single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus.
Its genome is about 11000 bases that codes for three structural proteins, capsid protein C, membrane protein M, envelope protein E; seven nonstructural proteins, NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5; and short non-coding regions on both the 5' and 3' ends.
Based on the analysis of the envelope protein there are at least four genotypes (1 to 4) - The American African genotype has been estimated to have evolved between 1907 to 1949. This period includes World War I and II which were associated with considerable movement of populations and environmental disturbance, factors known to promote the evolution of new vector borne viral species.
Until a few hundred years ago dengue virus was transmitted in sylvatic cycles in Africa and Asia between mosquitoes of the genus Aedes and non-human primates with rare emergences into human populations. The global spread of dengue virus, however, has followed its emergence from sylvatic cycles and the primary life cycle now exclusively involves transmission between humans and Aedes mosquitoes.
The reason that some people suffer from more severe forms of dengue, such as dengue hemorrhagic fever, is multifactorial. Among the possible causes are cross-serotypic immune response, through a mechanism known as antibody-dependent enhancement, which happens when a person who has been previously infected with dengue gets infected for the second, third or fourth time. The previous antibodies to the old strain of dengue virus now interfere with the immune response to the current strain, leading paradoxically to more virus entry and uptake.
There currently is no human vaccine available. Developing a vaccine against the disease is challenging. With...
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