INFLUENZA A VIRUSES

Table of contents :


  • Epidemiology
  • Genomics
  • Proteomics
  • Transmission
  • H1
  • H1N1
  • H1N7
  • H2
  • H2N2
  • H2N3
  • H2N8
  • H2N9
  • H3
  • H3N1
  • H3N2
  • H3N8
  • H4
  • H5
  • H5N1
  • H5N2
  • H5N3
  • H5N9
  • H6
  • H7
  • H7N1
  • H7N2
  • H7N3
  • H7N7
  • H8
  • H9
  • H9N2
  • H10
  • H11
  • H12
  • H13
  • H14
  • H15
  • H16
  • Pathogenesis
  • Symptoms & signs
  • Laboratory examinations
  • Therapy
  • Prevention
  • Web resources

  • Epidemiology : first described by Hippocrates in 412 b.C.. Different strains also infect Aves spp. (chickens, turkeys, ostriches (various AI virus strains have been isolated in recent years from clinically affected ostriches, in several countries. All but one were not poultry-pathogenic : the only reported clinical outbreak in ostriches caused by a poultry-pathogenic strain (HPAI) was recorded in Italy (H7N1)ref), quail, and peacocks; aquatic species : ducks, geese), Sus scrofa, Equus caballus, Phocidae, mustelids and Bos taurusref. Although viruses of relatively few subtype combinations have been isolated from mammalian species, all subtypes, in most combinations, have been isolated from birds.

    Genomics : 8 RNA segments. NIAID will invest $1 million to $2 million annually to sequence 500-1,000 influenza strains a year, each of them > 13,000 genetic letters long. The next step is to consult with scientists about which strains they would like to begin with and how to prioritize them. Robert Webster of St Jude Children's Research Hospital in Memphis, Tennessee, for example, is involved in the sequencing project and has a repository of over 12,000 bird flu strains collected over 27 years.
    Proteomics : 10 proteins + 1 facultative product
    Inside each envelope is a viral genome consisting of 8 negative-sense ssRNA segments of 890 to 2,341 nucleotides each. These segments are associated with nucleoprotein and 3 polymerase subunits, designated PA, PB1 and PB2; the resultant ribonucleoprotein complexes (RNPs) resemble a twisted rod (10–15 nm in width and 30–120 nm in length) that is folded back and coiled on itself. Late in viral infection, newly synthesized RNPs are transported from the nucleus to the plasma membrane, where they are incorporated into progeny virions capable of infecting other cells. TEM of serially sectioned virions shows that the RNPs of influenza A virus are organized in a distinct pattern (7 segments of different lengths surrounding a central segment). The individual RNPs are suspended from the interior of the viral envelope at the distal end of the budding virion and are oriented perpendicular to the budding tip. This finding argues against random incorporation of RNPs into virions, supporting instead a model in which each segment contains specific incorporation signals that enable the RNPs to be recruited and packaged as a complete set. A selective mechanism of RNP incorporation into virions and the unique organization of the eight RNP segments may be crucial to maintaining the integrity of the viral genome during repeated cycles of replicationref.
    Transmission : respiratory route. Human influenza virus replicates mainly in the upper respiratory tract and is usually readily transmitted via droplets formed during coughing or sneezing (B. R. Murphy, R. G. Webster, in Fields Virology, B. N. Fields et al., Eds. (Lippincott-Raven, Philadelphia, 1996), vol. 1, ch. 46). By contrast, the H5N1 influenza virus typically infects human cells in the lower respiratory tractref1, ref2 and so may be less easily shed from the infected patient; this may partly explain why so far there has been little human-to-human transmission observed.