Flavivirus

Flavivirus is a genus of enveloped, positive-sense RNA viruses in the Flaviviridae family. They are arthropod-borne (arboviruses), mainly transmitted by Aedes and Culex mosquitoes, with some tick-borne species. Notable human pathogens include dengue, yellow fever, Zika, West Nile, Japanese encephalitis, and tick-borne encephalitis viruses.

Genome and replication: Flaviviruses have a positive-sense single-stranded RNA genome roughly 10–11 kb long. The genome encodes a single polyprotein that's cleaved into structural proteins C, prM/M, E, and nonstructural proteins NS1–NS5. Virions are enveloped and icosahedral; replication occurs in cytoplasmic membrane-associated complexes.

Transmission and ecology: Transmission cycles differ by virus; many are spread by mosquitoes, others by ticks. Reservoirs include birds (West Nile), primates, and other wildlife; humans are usually incidental hosts for several species.

Clinical features: Infections range from asymptomatic to febrile illness. Dengue can cause dengue fever and, in some cases, dengue hemorrhagic fever or shock. Zika is typically mild but linked to congenital anomalies and Guillain–Barré syndrome. Yellow fever causes jaundice and hemorrhagic disease, while Japanese encephalitis and West Nile virus can cause encephalitis.

Diagnosis, treatment, and prevention: Diagnosis uses molecular tests (RT-PCR) and serology. There are no broadly effective antivirals; care is supportive. Prevention relies on vector control and vaccines for some flaviviruses, including yellow fever, Japanese encephalitis, and tick-borne encephalitis vaccines; dengue vaccines are used selectively in certain populations.

Taxonomy and notable species: The genus includes four dengue serotypes, West Nile, Zika, yellow fever, Japanese encephalitis, tick-borne encephalitis, Saint Louis encephalitis, and others. Flaviviruses share enveloped icosahedral virions and a positive-sense RNA genome.

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