Abstract
Reassortment events among influenza viruses occur naturally and may lead to the development of new and different subtypes which often ignite the possibility of an influenza outbreak. Between 2008 and 2010, highly pathogenic avian influenza (HPAI) H5 of the N1 subtype from the A/goose/Guangdong/1/96-like (Gs/GD) lineage generated novel reassortants by introducing other neuraminidase (NA) subtypes reported to cause most outbreaks in poultry. With the extensive divergence of the H5 hemagglutinin (HA) sequences of documented viruses, the WHO/FAO/OIE H5 Evolutionary Working Group clustered these viruses into a systematic and unified nomenclature of clade 2.3.4.4 currently known as “H5Nx” viruses. The rapid emergence and circulation of these viruses, namely, H5N2, H5N3, H5N5, H5N6, H5N8, and the regenerated H5N1, are of great concern based on their pandemic potential. Knowing the evolution and emergence of these novel reassortants helps to better understand their complex nature. The eruption of reports of each H5Nx reassortant through time demonstrates that it could persist beyond its usual seasonal activity, intensifying the possibility of these emerging viruses’ pandemic potential. This review paper provides an overview of the emergence of each novel HPAI H5Nx virus as well as its current epidemiological distribution.
Highlights
Wild aquatic birds have always been one of the recognized reservoirs and natural hosts of low pathogenic avian influenza (LPAI) viruses, and upon their circulation in domestic poultry, highly pathogenic variants of avian influenza viruses (AIVs) evolve [1,2,3,4,5,6,7,8]
The first reported case of highly pathogenic avian influenza (HPAI) viruses in domestic fowl was the 1878 Fowl Plague involving chickens in northern Italy [3,5,9]; since that plague, researchers’ perspectives of the biology of HPAI viruses—which emerged from LPAI viruses—have changed
One of the most potent viruses resulting from these biological changes was the HPAI H5N1 virus (A/goose/Guangdong/1/96, or Gs/GD), first isolated from a domestic goose in Guangdong Province, China in 1996 [2,9,10,11,12]
Summary
Wild aquatic birds have always been one of the recognized reservoirs and natural hosts of low pathogenic avian influenza (LPAI) viruses, and upon their circulation in domestic poultry, highly pathogenic variants of avian influenza viruses (AIVs) evolve [1,2,3,4,5,6,7,8]. One of the most potent viruses resulting from these biological changes was the HPAI H5N1 virus (A/goose/Guangdong/1/96, or Gs/GD), first isolated from a domestic goose in Guangdong Province, China in 1996 [2,9,10,11,12] This HPAI H5N1 Gs/GD lineage has developed multiple sublineages and has undergone reassortments with other AIVs [1,2,5]. By 2008, the second-order clades expanded into third-order clades with the development of 2.1.1–2.3.4 [19] This expansion was followed by a period with fewer outbreaks from 2009 to 2013 [2]. These viruses could have been displaced by new clades, as they appear to be extinct [22]
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