Rapid Emergence of Highly Pathogenic Avian Influenza Subtypes From a Subtype H5N1 Hemagglutinin Variant

Emerg Infect Dis. 2015 May;21(5):842-6. doi: 10.3201/eid2105.141927.


In 2014, novel highly pathogenic avian influenza A H5N2, H5N5, H5N6, and H5N8 viruses caused outbreaks in Asia, Europe, and North America. The H5 genes of these viruses form a monophyletic group that evolved from a clade 2.3.4 H5N1 variant. This rapid emergence of new H5Nx combinations is unprecedented in the H5N1 evolutionary history.

Keywords: H5N1; HPAI; avian influenza; clade 2.3.4; evolution; hemagglutinin; highly pathogenic; influenza; monophyletic group; rapid emergence; reassortant; reassortment events; subtype; variant; virulent; viruses.

MeSH terms

  • Animals
  • Disease Outbreaks
  • Genetic Variation*
  • Genotype
  • Hemagglutinins / genetics*
  • Humans
  • Influenza A Virus, H5N1 Subtype / genetics*
  • Influenza A Virus, H5N1 Subtype / pathogenicity
  • Influenza A virus / classification*
  • Influenza A virus / genetics*
  • Influenza A virus / pathogenicity
  • Influenza in Birds / virology*
  • Influenza, Human / virology*
  • Phylogeny
  • Poultry
  • Reassortant Viruses / classification
  • Reassortant Viruses / genetics


  • Hemagglutinins