Flavivirus is a genus of the family Flaviviridae. This genus includes the West Nile Virus, Dengue Virus, Tick-borne Encephalitis virus, yellow fever virus, and quite a few others. Flaviviruses get their name from the yellow fever virus. Flavus means yellow in Latin. Yellow fever was named because if caused yellow jaundice in victims.

Mosquitoes and ticks transmit these viruses by biting people. Human infections are usually incidental since humans are unable to replicate the virus. Yellow fever and dengue viruses are the exceptions to this rule although they still require mosquito vectors.

The virus can also be transmitted via handling animal carcasses, blood transfusion, child birth, and through consumption of un-pasteurized milk products.