Flaviviridae is a family of single-stranded RNA-containing viruses that mostly cause hemorrhagic fever in a wide range of mammals and are often transmitted by mosquitos and ticks. Of the 70 members of this family, 13 cause diseases in humans, typically hemorrhagic fevers, hepatitis, or encephalitis.

Members of this viral family include:

Genus Flavivirus
Genus Hepacivirus
Genus Pestivirus
  • the pestiviruses (which cause animal diseases like diarrhea in cows but no known human ailments, though it's always possible for viruses to mutate and spread to new hosts)

The family gets its name from its first-identified member, yellow fever, since the Latin word for "yellow" is flavus. Most flaviviruses are classified as group B arboviruses. Until 1984, flaviviruses were lumped in with the togavirus family, but replication differences warranted giving them a separate family.

These viruses superficially resemble togaviruses: they are spherical, have a rough envelope, and are 40-60 nanometers in diameter. Each has an icosahedral nucleocapsid that is 25-30 nm in diameter. The virus' genome is made up of a linear, single strand of positive-sense RNA that is about 11000 nucleotides long. Its gene sequence is very similar to that of the picornavirus, and its sequence homology is quite similar to that of the tobacco mosaic virus.

The viruses replicate themselves in the cell's cytoplasm. In flaviviruses, the replication takes 20-30 hours total, so the onset of disease after infection can take a day to several days.

Most of these virus infections are not treated with antiviral medications (except for hepatitis C, which can be treated with alpha interferon or ribavarin). Although diseases like yellow fever can be severe, most infections clear up on their own, so medical assistance is generally supportive (providing fluids to prevent dehydration from diarrhea and vomiting, medicine to reduce fever, etc.)

Vaccination is the best strategy to deal with these diseases. So far, vaccines have been developed for yellow fever and tick-borne encephalitis. There is a vaccine for Japanese encephalitis that is not approved for use in the U.S. yet, and a vaccine for dengue is being developed.

For other illnesses such as the West Nile virus, the best tactic to avoid infection is to avoid infection. People going outdoors in areas known to have reservoirs of the viral diseases should wear long sleeves, long shirts, and insect repellent. Furthermore, people should avoid drinking milk from farm animals that seem to be ill.

Hepatitis is only very rarely transmitted by insect bites; sexual contact and blood contact from infected people remain the primary routes of infection. Thus, people should use condoms when having sex with partners of unknown health status and should never share or re-use hypodermic needles.