The Flaviviridae family consists of enveloped viruses that adopt icosahedral structures. They have a positive sense, single-strand RNA genome that is transcribed as a single polyprotein.  More than 100 different members of the Flaviviridae are known, and are subdivided into Flavivirus (including dengue, yellow fever, and West Nile viruses), Pestivirus, and Hepacivirus (hepatitis C viruses) genera. These genera have diverse biological properties and cause distinct diseases. However, they have similar genome organization and replication mechanisms. Based on sequence similarity and mode of transmission, the 70 viruses within the flavivirus genus separate into distinct mosquito- and tick-borne serocomplexes. These viruses show sequence homologies typically >40%. The hepaciviruses are blood-borne viruses, and include the many strains of hepatitis C viruses.

Flaviviridae phylogenetic tree (unrooted)

Flavivirus polyprotein structure

The flavivirus genome consists of a ~11kb single-stranded positive-sense RNA. Following infection, the viral genome is directly translated into a single polyprotein by host cell proteins.  The polyprotein undergoes post-translational cleavage by viral and cellular proteases to generate three structural proteins (capsid, membrane, and envelope) and seven nonstructural proteins  (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). The nonstructural proteins are required for virus replication.  The N-terminus of NS3  codes a serine protease essential for virus replication. The central domain of NS2B serves as co-factor for the NS3 serine protease.