Members of the family Flaviviridae are positive-strand RNA viruses. Genomes are unsegmented and range in size from 9.5 to 12.5 kb. The genome serves as the single mRNA and all viral proteins are synthesized as part of a large polyprotein precursor. (Translation is interesting as some of the polyprotein is targeted to endoplasmic reticulum while other parts remain cytosolic.) Genomes are not polyadenylated but instead have a hairpin structure at the 3′ end. Virions are enveloped with a diameter of about 30 nm. A single capsid protein (C) assembles to form the capsid. Two or three glycoproteins are associated with the envelope. Flaviviruses have a unique morphology for enveloped viruses, as the glycoproteins lie flat on the surface of the mature virion, giving it a golf-ball-like appearance. There are four genera in the family Flaviviridae and three of these contain important human and animal pathogens. The genus Hepacivirus contains the human Hepatitis C virus, a blood-borne pathogen. In contrast members of the genus Flavivirus are transmitted by insects (often mosquitos) and they have evolved to replicate in both animal and insect hosts. They include Yellow fever virus, Dengue virus, West Nile virus, and Zika virus. Within the genus Pestivirus are important pathogens of food animals.