Flaviviruses (Dengue, Yellow Fever, Japanese Encephalitis, West Nile Encephalitis, Usutu Encephalitis, St. Louis Encephalitis, Tick-Borne Encephalitis, Kyasanur Forest Disease, Alkhurma Hemorrhagic Fever, Zika)

The flaviviruses are a family of small, enveloped, RNA viruses, many of which can cause acute infections in humans. Yellow fever, dengue, Japanese encephalitis, West Nile, tick-borne encephalitis, and Zika viruses are the most clinically important of these viruses; however, other members of this family have caused outbreaks of disease and have the potential for emergence. Flaviviruses are transmitted between arthropod and vertebrate hosts; their geographic distribution and risk for acquisition largely reflect that of the invertebrate (mosquito or tick) host. The clinical presentation includes systemic febrile illness, plasma leakage/hemorrhagic fever syndrome, and central nervous system disease, but most infections are unrecognized. Zika virus is unique in its potential for sexual (person-to-person) transmission and for maternal-fetal transmission with severe congenital neurologic disease. Definitive diagnosis relies on detection of viral RNA or antigen in blood during the acute febrile phase (days 1-5) or on detection of specific IgM antibody thereafter. Antigenic cross-reactivity across the family complicates the interpretation of serologic data, however. Therapy consists of supportive care appropriate for the clinical syndrome. Avoidance of exposure is the primary approach to prevention. Vaccines are available for yellow fever, Japanese encephalitis, and tick-borne encephalitis viruses. A vaccine for dengue was recently licensed but can only be used in individuals who have had a previous infection with dengue virus.