Flavivirus
The genus Flavivirus comprises enveloped viruses with a positivsträngigen single-stranded RNA as a genome, which are transmitted by arthropods ( ticks and mosquitoes ) as vectors on birds and mammals. The name of the genus and of the whole virus family Flaviviridae is derived from the yellow fever virus in humans from (from Latin flavus, "yellow" ), which was recognized in 1904 transferred from Walter Reed as by mosquitoes.
Virus of the genus Flavivirus cause important diseases in animals and humans. Among these diseases, which correspond to a viral haemorrhagic fever or are characterized by an infection of the central nervous system in the sense of encephalitis, meningoencephalitis or Leukenzephalitis. These are in addition to the yellow fever, for example, the tick-borne encephalitis ( TBE ), Japanese encephalitis, dengue fever and West Nile fever.
Morphology
The virions of flaviviruses are about 50 nm in diameter in size and in the electron microscopic appearance of spherical, irregular shape. Analysis by cryo- electron microscopy showed an icosahedral symmetry of the virus envelope, which suggests the capsid proteins to an interaction of the envelope proteins in the dengue virus. The capsid is made of only a capsid protein ( C, 11 kDa) built. In the viral envelope of the virion 90 dimers of the E protein (50 kDa) are embedded. Between this network of e- dimers there is another, smaller envelope protein ( M protein, 26 kDa).
Genome organization
Positivsträngige the RNA about 11,000 nucleotides in length and contains only one open reading frame that encodes for a polyprotein. Host proteases cut this polyprotein own in the three structural (C, prM, E) and in the seven non-structural proteins ( NS1, NS2A, NS2B, NS3, NS4A, NS4B, NS5 ); the list corresponds to the arrangement of the coding for the proteins of genes on the genome. In contrast to the other genera of the Flaviviridae family viruses of the genus Flavivirus in the 5'- end of the RNA having a 5 'cap structure of the type 1 (m- 7GpppAmp ) followed by a conserved dinucleotide AG. At the 3'- end can be found in flaviviruses as opposed to the other genera no poly (A ) tail.
Replication
The viruses infect amongst others monocytes, macrophages and dendritic cells. They attach to via specific receptors on the cell surface and are taken up by a ausbildendes to Endosomvesikel. Inside the endosome, the acidic pH induces the fusion of endosome membrane and the viral envelope. Thus, the capsid reaches the cytosol, decays and releases the genome freely. Both the receptor binding and membrane fusion are catalyzed by the protein E, which a conformational change lives at acidic pH, which means that the 90 homodimers reorganize to 60 homotrimers.
After penetration into the host cell, the viral genome is replicated in the rough ER and in so-called vesicle packets. Within the ER an immature form of the virus particle is first produced, in which the M protein was not cleaved by a maturation step and present as prM ( precursor M) in a complex with E. The immature particles are processed in the Golgi apparatus by the host protein furin, which cleaves prM to M. Thus E is released from the complex and can take its place in the mature, infectious virion.
Transmission
Flaviviruses can also be transmitted directly from one vertebrate to another indirectly by blood-sucking insects or, in rare cases ( for example, when Rio Bravo virus). Some flaviviruses circulate between rodents and bats without known another vector.
System
The viruses of the genus Flavivirus was formerly distinguished by their transmission by arthropods ( arthropods ) as arbovirus group B of the group A arboviruses, which later became the alphavirus genus of the Togaviridae family emerged.
The genus Flavivirus includes 53 species of virus (as of 2009 ), a total of 73 serotypes distinguished. According to the type of vector (mosquito, tick ), an unknown vector (NAB Group: no known vector) and on the basis of phylogenetic studies, the species are grouped together in groups ( non- taxonomic ).
1 Tick-borne flaviviruses
- Species Gadgets Gully virus
- Species Kyasanur Forest Disease Virus
- Species Louping - Ill virus
- Species Omsk hemorrhagic fever virus
- Species Powassan virus
- Species Royal Farm virus
- Species TBE virus
- Species Kadam virus
- Species Méaban virus
- Species Saumarez Reef virus
- Species Tyuleniy virus
Mosquito-borne flaviviruses 2
- Species Aroa virus
- Species Dengue virus
- Species Kedougou virus
- Species Cacipacore virus
- Species Japanese encephalitis virus
- Species Koutango virus
- Species Murray Valley encephalitis virus
- Species St. Louis encephalitis virus
- Species Usutu virus
- Species West Nile virus
- Species Kokobera virus
- Species Bagaza virus
- Species Ilheus virus
- Species Israel turkey meningoencephalitis virus
- Species Ntaya virus
- Species Tembusu virus
- Species Zika virus
- Species Banzi virus
- Species Bouboui virus
- Species Edge Hill virus
- Species Yugra virus
- Species Saboya virus
- Species Sepik virus
- Species Uganda S virus
- Species Wesselsbron virus
- Species yellow fever virus
3 flaviviruses with unknown vector
- Species Entebbe bat virus
- Species Yokose virus
- Species Apoi virus
- Species Cowbone Ridge virus
- Species Jutiapa virus
- Species Modoc virus
- Species Sal Vieja virus
- San Perlita species virus
- Species Bukalasa bat virus
- Species Carey Iceland virus
- Species Dakar bat virus
- Species Montana Myotis Leukenzephalitis virus
- Phnom Penh species - bat virus
- Species Rio Bravo virus
Non- classified species within the genus Flavivirus:
- Species Tamana bat virus
Swell
- H.-J. Thiel, M. S. Collett et al. Genus Flavivirus. In: CM Fauquet, MA Mayo et al.: Eighth Report of the International Committee on Taxonomy of Viruses. London, San Diego, 2005 ISBN 0-12-249951-4
- D. Gubler, G. Kuno, L. Markoff: Flaviviruses. In: David M. Knipe, Peter M. Howley ( ed. -in- chief): Fields' Virology. 5th Edition, Volume 1, Philadelphia 2007, pp. 1153ff ISBN 0-7817-6060-7
- Gould EA, Solomon T. Pathogenic flaviviruses. Seminar. Lancet 2008; 371:500-9