Neurotropic Flaviviruses

Abstract

Flaviviruses are small, positive-strand RNA viruses in the genus Flavivirus within the Flaviviridae family. The Flavivirus genus consists of nearly 80 viruses, approximately half of which are associated with human disease. The majority of flaviviruses are arthropod-borne viruses, or arboviruses, transmitted from infected to susceptible vertebrate hosts primarily by mosquitoes and ticks. Flavivirus infections cause seasonal disease syndromes corresponding to mosquito and tick activity throughout the temperate and tropical areas of the world. Medically important flaviviruses are associated with three clinical syndromes: encephalitis and meningitis; hemorrhagic fever; or fever, arthralgia, and rash. The neurotropic flaviviruses that cause neuroinvasive disease belong primarily to two groups: mosquito-borne viruses in the Japanese encephalitis serocomplex and tick-borne viruses in the tick-borne encephalitis serogroup. The most important human pathogens in these two groups in terms of number of cases include Japanese encephalitis virus, West Nile virus, St. Louis encephalitis virus, and Murray Valley encephalitis virus in the Japanese encephalitis serocomplex; in the tick-borne encephalitis serocomplex, Powassan virus and tick-borne encephalitis virus subtypes Far Eastern, Siberian, and European. In this chapter the general features of the neurotropic flaviviruses will be reviewed. Clinical disease syndromes, epidemiological and ecological aspects, as well as prevention strategies of specific medically important flaviviruses will be described in individual sections at the end of the chapter, with the exception of Japanese encephalitis virus, which will be presented in chapter “Borna Disease Virus.” Dengue viruses, which usually cause febrile illness or hemorrhagic manifestations, occasionally present as meningoencephalitis, and are discussed in chapter “Neurotropic Influenza Virus Infections.”