Flavivirus

Flavivirus is a genus of the family Flaviviridae. This complex includes the West Nile virus, dengue virus, Tick-borne Encephalitis Virus, Yellow Fever Virus, and several other viruses which cause encephalitis.

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Flavivirus share a common size (40-65 nm), symmetry (enveloped, icosahedral nucleocapsid), nucleic acid (positive-sense, single stranded RNA approximately 10,000-11,000 bases), and appearance in the electron microscope. Rats carry flavivirues, but whether they can transmit them is in question.

Replication

Flavivirus have a (+) sense RNA genome and replicate in the cytoplasm of the host cells. The genome mimics the cellular mRNA molecule in all aspects except for the absence of the poly-adenylated (poly-A) tail. This feature allows the virus to exploit cellular apparatus to synthesise both structural and non-structural proteins, during replication. The cellular ribosome is crucial to the replication of the flavivirus, as it translates the RNA, in a similar fashion to cellular mRNA, resulting in the synthesis of a single polyprotein.

Once translated, the polyprotein is cleaved by a combination of viral and host proteases to release mature polypeptide products. Nevertheless, cellular post-translational modification is dependent on the presence of a poly-A tail; therefore this process is not host-dependent. Instead, the polyprotein contains an autocatalytic feature which automatically releases the first peptide, a virus specific enzyme. This enzyme is then able to cleave the remaining polyprotein into the individual products. One of the products cleaved is a polymerase, responsible for the synthesis of a (-) sense RNA molecule. Consequently this molecule acts as the template for the synthesis of the genomic progeny RNA.

New viral particles are subsequently assembled. This occurs during the budding process which is also responsible for the accumulation of the envelope and cell lysis.

Species

• Genus Flavivirus
  • Tick-borne viruses
    • Mammalian tick-borne virus group
      • Gadgets Gully virus (GGYV)
      • Kadam virus (KADV)
      • Kyasanur Forest disease virus (KFDV)
      • Langat virus (LGTV)
      • Omsk hemorrhagic fever virus (OHFV)
      • Powassan virus (POWV)
      • Royal Farm virus (RFV)
      • Tick-borne encephalitis virus (TBEV)
      • Louping ill virus (LIV)
    • Seabird tick-borne virus group
      • Meaban virus (MEAV)
      • Saumarez Reef virus (SREV)
      • Tyuleniy virus (TYUV)
  • Mosquito-borne viruses
    • Aroa virus group
      • Aroa virus (AROAV)
    • Dengue virus group
      • Dengue virus (DENV)
      • Kedougou virus (KEDV)
    • Japanese encephalitis virus group
      • Cacipacore virus (CPCV)
      • Koutango virus (KOUV)
      • Japanese encephalitis virus (JEV)
      • Murray Valley encephalitis virus (MVEV)
      • St. Louis encephalitis virus (SLEV)
      • Usutu virus (USUV)
      • West Nile virus (WNV)
      • Yaounde virus (YAOV)
    • Kokobera virus group
      • Kokobera virus (KOKV)
    • Ntaya virus group
      • Bagaza virus (BAGV)
      • Ilheus virus (ILHV)
      • Israel turkey meningoencephalomyelitis virus (ITV)
      • Ntaya virus (NTAV)
      • Tembusu virus (TMUV)
    • Spondweni virus group
      • Zika virus (ZIKV)
    • Yellow fever virus group
      • Banzi virus (BANV)
      • Bouboui virus (BOUV)
      • Edge Hill virus (EHV)
      • Jugra virus (JUGV)
      • Saboya virus (SABV)
      • Sepik virus (SEPV)
      • Uganda S virus (UGSV)
      • Wesselsbron virus (WESSV)
      • Yellow fever virus (YFV)
  • Viruses with no known arthropod vector
    • Entebbe virus group
      • Entebbe bat virus (ENTV)
      • Yokose virus (YOKV)
    • Modoc virus group
      • Apoi virus (APOIV)
      • Cowbone Ridge virus (CRV)
      • Jutiapa virus (JUTV)
      • Modoc virus (MODV)
      • Sal Vieja virus (SVV)
      • San Perlita virus (SPV)
    • Hepatitis C virus (HCV)
    • Rio Bravo virus group
      • Bukalasa bat virus (BBV)
      • Carey Island virus (CIV)
      • Dakar bat virus (DBV)
      • Montana myotis leukoencephalitis virus (MMLV)
      • Phnom Penh bat virus (PPBV)
      • Rio Bravo virus (RBV)

References

• Phylogeny of the genus Flavivirus. - Kuno G, Chang GJ, Tsuchiya KR, Karabatsos N, Cropp CB. J Virol. 1998 Jan;72(1):73-83.
• Population dynamics of flaviviruses revealed by molecular phylogenies. - Zanotto PM, Gould EA, Gao GF, Harvey PH, Holmes EC. Proc Natl Acad Sci U S A. 1996 Jan 23;93(2):548-53.
• Molecular Biology of the Flavivirus. - Matthias Kalitzky, Taylor & Francis Ltd 2005 Oct 5; ISBN 190493322X