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| Recent H5 Detections Around The Globe - Credit WHO |
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Influenza A viruses are broadly categorized by two proteins they carry on their surface; their HA (hemagglutinin) and NA (neuraminidase), resulting in subtypes like H5N1, H7N9, or H3N2.
Within each subtype there are genetic groupings called clades, and often within each clade - subclades – and within each of these, many variants may exist. Continual antigenic drift, host adaptations, and repeated reassortments, have - over the past two decades - made the HPAI H5's family tree very complex (see below).
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| Credit WHO |
The (clade 0) HPAI H5N1 virus that appeared more than 20 years ago in Hong Kong has been long replaced by a series of newer, more `biologically fit' versions.
Clade 1 viruses which appeared in 2003 - mostly in Vietnam, Cambodia & Thailand - have now given way to clade 2 viruses around the globe (see WHO chart at top of this blog).
In 2005, during the first major expansion of H5N1 beyond Southeast Asia, we saw a massive die off of birds at Qinghai Lake in China (see H5N1 Influenza Continues To Circulate and Change 2006 by Webster et. al.). Suddenly, and unexpectedly, waterfowl (brown headed gulls, cormorants, ducks, geese, etc.) died by the thousands from the H5N1 virus.
What emerged at Qinghai Lake - and quickly spread into Europe, Africa, and the Middle east - was clade 2.2 (aka QH05) of the H5N1 virus.In 2009 researchers found evidence of another clade (2.3.2) (see 2011 EID Journal New Avian Influenza Virus (H5N1) in Wild Birds, Qinghai, China), which was detected in dead birds in the same region. In short order the 2.3.2 clade began to show up in migratory birds, and poultry, from Japan to India, supplanting the old 2.2 clade in many regions.
Clade 2.2.1.2 viruses circulate widely in Egypt and clade 2.3.2.1a are occasionally reported in India and Bangladesh, but the two most active HPAI H5 clades today are clade 2.3.4.4 and clade 2.3.2.1c.Clade 2.3.4.4 H5 viruses have become notorious for their ability to reassort and reinvent themselves into new subtypes (including H5N1, H5N2, H5N5, H5N6, H5N8, and H5N9) - but all of the known clade 2.3.2.1c viruses have been of only one subtype; H5N1.
Until now.This week the ASM journal Microbiology has published the details on the first reassortant clade 2.3.2.1c H5N6 to be detected, isolated from a wild bird in China back in 2016.
Today's report is a reminder that HPAI H5 viruses continue to evolve in the wild, and while this new virus did not show many of worrisome mammalian adaptions that have been seen with clade 2.3.4.4 H5N6, it is another uncertain evolutionary pathway for the virus to follow.I've only included a few excerpts from the announcement, so follow the link below to read it in its entirety.
First Detection of a Novel Reassortant Avian Influenza A(H5N6) Clade 2.3.2.1c Virus, Isolated from a Wild Bird in China
Tao Zhang, Ruiyun Li, Gaodong Zhu, Jianyu Chang, Bing Xu
Simon Roux, Editor
ABSTRACT
We report the first isolation of a reassortant clade 2.3.2.1c avian influenza A(H5N6) virus isolated from a wild bird sample in Jiangxi, China, in 2016. Sequence analyses indicated that this virus most likely evolved from Eurasia-derived H5N1 and H6N6 viruses through frequent interactions at the wild-domestic bird interface.
ANNOUNCEMENT
Avian influenza virus (AIV) is a single-stranded segmented negative-sense RNA virus classified in the Alphainfluenzavirus genus in the family Orthomyxoviridae (1). The hemagglutinin (HA) gene of highly pathogenic avian influenza (HPAI) A(H5) viruses has undergone continuous evolution, generating emerging reassorted subtypes and clades (2). Among these variants, two relatively new clades, i.e., 2.3.4.4 and 2.3.2.1c, predominately shaped the current viral evolution and transcontinental expansions (3, 4).
It is remarkable that clade 2.3.4.4 involves multiple subtypes, including H5N1, H5N2, H5N6, and H5N8 (2). In contrast, all clade 2.3.2.1c viruses, including the novel Sanmenxia clade 2.3.2.1c-like H5N1 virus isolated in a wild bird, belong to H5N1 (5).
Here, we provide a report on the first detection and nearly complete genome sequence of a novel reassortant clade 2.3.2.1c H5N6 sample isolated from a wild bird in China.
(SNIP)
This detection suggests continuous reassortment and generation of emerging variants. Further investigation and active surveillance are required to detect new AIV variants.
Data availability.The genome sequence of Jiangxi clade 2.3.2.1c H5N6 virus has been deposited in GenBank with the accession numbers MN165550 to MN165557.
