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Flaviviruses excluding dengue 

Flaviviruses excluding dengue

Chapter:
Flaviviruses excluding dengue
Author(s):

E.E. Ooi

, L.R. Petersen

, and D.J. Gubler

DOI:
10.1093/med/9780199204854.003.070514_update_001

Update:

New flaviviruses.

Epidemiology and ecology—new information on vector and reservoir species.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 25 March 2017

Flaviviruses, family Flaviviridae, are enveloped viruses with a single-strand positive-sense RNA genome approximately 11 kb in length. They comprise 53 species (40 of which can cause human infection), divided into three major groups based on epidemiology and phylogenetics. They are maintained in nature in complex transmission cycles involving a variety of animals and hematophagous arthropods, which transmit infection to humans. IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) is widely used for diagnosis, with confirmation requiring a four-fold or greater rise in specific antibodies between acute and convalescent serum samples, virus isolation, detection of specific antigen by immunohistochemistry or of viral RNA by nucleic acid amplification from blood or other tissue sample.

Mosquito-borne flaviviruses

Dengue and dengue haemorrhagic fever (see Chapter 7.5.15) is the most important and widespread human disease caused by an arbovirus, causing a broad spectrum of illness ranging from asymptomatic to severe and fatal haemorrhagic disease. It is primarily an urban disease transmitted among humans by the highly domesticated Aedes aegypti mosquito.

Japanese encephalitis virus—has a widespread distribution throughout Asia; is the most important cause of arboviral encephalitis; is maintained in a cycle involving Culex mosquitoes and water birds; about 1/250 infections are symptomatic, with manifestations ranging from a febrile illness with headache, through aseptic meningitis, to encephalitis, and death. Many survivors have residual neurological abnormalities. There is no specific treatment. Vaccination should generally be offered to people spending a month or more in endemic areas, especially if travel includes rural areas.

St Louis encephalitis virus—prevalent throughout the western hemisphere from southern Canada to Argentina; maintained in a cycle involving Culex mosquitoes and water birds; 1/16 to 1/425 infections are symptomatic, with manifestations ranging from fever with headache, to aseptic meningitis, to encephalitis, and death. There is no specific treatment. No vaccine is available.

West Nile virus—found in Africa, the Middle East, Asia, Australia (Kunjin is a subtype of West Nile virus), parts of Europe and the Americas; maintained in a cycle involving Culex mosquitoes and water birds; most infections are asymptomatic, but 20% develop a febrile illness, and 1% neuroinvasive disease including meningitis, encephalitis and acute flaccid paralysis. There is no specific treatment. Several equine vaccines are available, and human vaccines are in clinical trials.

Yellow fever virus—found in tropical America and Africa; forest/jungle transmission cycle involves canopy-dwelling mosquitoes and monkeys, urban cycle involves humans as the vertebrate host and Aedes aegypti as the principal vector; 5% of infections present clinically with a viraemic illness, which may be followed after a transient period of remission by relapse with shock, neurological deterioration, jaundice, haemorrhagic manifestations and renal failure. Treatment is symptomatic. A live, attenuated, single-dose vaccine is highly effective.

Other important mosquito-borne flaviruses include Murray Valley, Rocio and Zika virus.

Tick-transmitted flaviviruses

Tick-borne encephalitis, louping ill, Powassan encephalitis—geographical distribution determined by that of relevant hard tick vectors; rodents are the principal vertebrate hosts, with occupational and vocational pursuits favouring tick exposure as risk factors for human disease; most infections are subclinical, but a nonspecific influenza-like illness may be followed, after a few days of apparent recovery, by aseptic meningitis or meningoencephalitis that may lead to permanent paralysis in some cases. Treatment is supportive. Effective inactivated vaccines are available.

Tick-borne haemorrhagic fevers—these include Kyasanur Forest disease and Alkhumra (strictly Al Khumra) and Omsk haemorrhagic fevers.

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