Background
Since highly pathogenic avian influenza (HPAI) H5N1 viruses were first identified in humans in 1997, they
have evolved rapidly and have formed multiple distinct genetic clades. During this time HPAI viruses have
caused millions of deaths among birds and over six hundred deaths in humans.
Laboratory studies have implicated convergent evolution of certain molecular determinants for
pathogenicity and host specificity for influenza viruses in nature; however, our understanding of the precise
molecular determinants required for transmissibility and severe disease in mammals remains incomplete.
It is believed that there are likely to be multiple evolutionary pathways that would increase mammalian
transmissibility of avian influenza viruses, including HPAI H5N1 viruses.
In light of the expanding host range, geographic spread, and the effect of co-circulation of heterogeneous
viruses on interspecies transmission of H5N1 viruses, it is critical that enhanced approaches to influenza
surveillance are maintained. Early detection of the natural emergence of genetic changes that may enhance
adaptation of HPAI H5N1 viruses for humans and/or other mammals or may impair antiviral interventions
is an essential component of this effort. The WHO Collaborating Center for Influenza Reference and
Research at the Centers for Disease Control and Prevention in Atlanta, with input from many influenza
subject matter experts from around the world, has developed an inventory of amino acid mutations in
H5N1 viruses that is intended to be used by the influenza surveillance and research community as a tool to
inform the influenza knowledge base for surveillance and public health preparedness.
Continued - Click on Title for Link
6-21-2012
Version 1.0
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