EID Journal Home > Volume 14, Number 7?July 2008
Volume 14, Number 7?July 2008
Online Report
Toward a Unified Nomenclature System for Highly Pathogenic Avian Influenza Virus (H5N1)
WHO/OIE/FAO H5N1 Evolution Working Group1
snip
As other studies have shown, the primary clade defining factor appears to be spatio-temporal because most distinct clades consist of isolates within close geographic proximity to one another or from specific time periods (perhaps as a result of heightened transmission during outbreak periods) (2?7). Notably, clade 2.2 comprises isolates from more widespread geographic areas (3 continents), which is likely to reflect movement of the virus through long-distance spread as a result of poultry trade or wild bird migration (2,3,6,7).
The evolution of the H5 HA in avian hosts shows a notable difference from the typical evolution of HA genes from human influenza viruses. The evolution of the H3 HA since 1968 is characterized by a limited diversity among circulating strains. This lack of diversity is clearly the consequence of rapid extinction after the emergence of new clades and lineages.
As expected, the evolutionary tree of human influenza HA genes has extended trunks and extremely short branches (14,15). In contrast, multiple avian influenza A HA clades continue to evolve and co-circulate in different regions and species; hence, the unprecedented need for a nomenclature system that has been unnecessary for human influenza genes.
The results from this study indicate that the HPAI H5N1 viruses can be grouped into several clades designated by a numbering system that can continue to be expanded as these viruses continue to evolve. By establishing this nomenclature system and guidelines for naming clades, this information can be used in the future as criteria for assigning new clades as new lineages of HPAI H5N1 variants emerge.
Volume 14, Number 7?July 2008
Online Report
Toward a Unified Nomenclature System for Highly Pathogenic Avian Influenza Virus (H5N1)
WHO/OIE/FAO H5N1 Evolution Working Group1
snip
As other studies have shown, the primary clade defining factor appears to be spatio-temporal because most distinct clades consist of isolates within close geographic proximity to one another or from specific time periods (perhaps as a result of heightened transmission during outbreak periods) (2?7). Notably, clade 2.2 comprises isolates from more widespread geographic areas (3 continents), which is likely to reflect movement of the virus through long-distance spread as a result of poultry trade or wild bird migration (2,3,6,7).
The evolution of the H5 HA in avian hosts shows a notable difference from the typical evolution of HA genes from human influenza viruses. The evolution of the H3 HA since 1968 is characterized by a limited diversity among circulating strains. This lack of diversity is clearly the consequence of rapid extinction after the emergence of new clades and lineages.
As expected, the evolutionary tree of human influenza HA genes has extended trunks and extremely short branches (14,15). In contrast, multiple avian influenza A HA clades continue to evolve and co-circulate in different regions and species; hence, the unprecedented need for a nomenclature system that has been unnecessary for human influenza genes.
The results from this study indicate that the HPAI H5N1 viruses can be grouped into several clades designated by a numbering system that can continue to be expanded as these viruses continue to evolve. By establishing this nomenclature system and guidelines for naming clades, this information can be used in the future as criteria for assigning new clades as new lineages of HPAI H5N1 variants emerge.