Lancet Microbe: Novel Human-Type Receptor-Binding H5N1 Virus in Live Poultry Markets, China

Flu Virus binding to Receptor Cells – Credit CDC

18,483

While there are a number of known barriers the H5Nx virus must overcome before it can transmit efficiently between humans, arguably the biggest, and most important, is developing the ability to bind to α2,6 receptor cells commonly found in the human respiratory system.

As an avian virus, H5Nx binds preferentially to α2,3 receptor cells, which are abundant in the gastrointestinal tract of birds.

We've discussed receptor binding before, but briefly:

α2,3-linked and α2,6-linked receptor cells have stalks of sugar (carbohydrate) molecules on their surface. These carbohydrate molecules - called `glycans' - form a dense sugary coating to all animal cell membranes. The composition of these stalks varies between types of cells and hosts.

When a virus meets a compatible receptor cell, they are able to `dock', allowing the virus to enter the cell.

Humans, and many (but not all) mammals have very few α2,3 receptor cells in their upper airway (but do have some deep in the lungs), making it difficult for avian flu viruses to easily attach to, and infect, non-avian species.

Over the years we've looked at a number of mutations that could switch binding preferences, and amino acid changes at HA position 193 have come up repeatedly (see 2018's JVI: K193T Mutation Enhances Human-type Receptor Binding In Ferret Transmissible H5N1). 

Last January, in Emerg. Microb. & Inf.: HA N193D Substitution Alters Receptor Binding Affinity & Enhances Virulence in Mammalian Hosts we saw a report out of South Korea on the discovery of a `distinct mutation' (a change from Asparagine (N) to Aspartic acid (D)) at position 193 of the HA in a number of H5N1 isolates collected from wild birds in 2021-2022. The authors noted:

Variations at position 193 of the HA protein exhibit profound implications for influenza viruses, notably, mutations at this position were reported to have an effect on virus adaptability across influenza subtypes, including H5, H3, H7, H9, and H10 [22-27]. The presence of mutations in the HA-193 confers a shift in the receptor binding preference of the virus α2,3 to α2,6 sialic acid or vice versa.  

Today we have a correspondence from Chinese researchers who report finding two concerning mutations - (D158N and N193K) - in poultry markets in Poyang Lake (Jiangxi Province) earlier this year.  Both mutations are known to facilitate binding to α2,6 (human) receptor cells.

The H5N1 virus was identified as being clade 2.3.4.4b, which is the same clade which has spread globally over the past 4 years.

While less well studied, the D158N mutation was identified in a fatal human H5N1 infection in Turkey, back in 2006 (see Mutations in Influenza A Virus(H5N1) and Possible Limited Spread, Turkey, 2006). 

The detection of similar α2,6 adaptive mutations - first in wild birds, then in poultry - two years and 1000 km apart in Asia, is something that needs to be monitored closely. 

The link and text to the correspondence follows:

Correspondence

Novel human-type receptor-binding H5N1 virus in live poultry markets, China

Feng Wen a, Yu Yang a, Yong Li b, Jinyue Guo a, Zhili Li a, Lian Liu a, Hao Liu a, Kun Mei a, Limei Qin a, Keshan Zhang a, Tao Ren c, Shujian Huang aShow more
https://doi.org/10.1016/j.lanmic.2024.101049 
Under a Creative Commons license

Avian influenza viruses represent a considerable public health risk, with the capability to cross species barriers and cause severe disease in humans. The emergence of H5N1 subtype of highly pathogenic avian influenza viruses has been particularly concerning because it has caused numerous poultry outbreaks and sporadic human infections, including cases in dairy cows in 2024.1 

As of April, 2024, H5N1 infections have resulted in 463 deaths, corresponding to a mortality rate of 52%,2 thereby heightening concerns about its pandemic potential. Live poultry markets (LPMs) are recognised as a major source of human H5N1 infections.3 The emergence of H5N1 viruses with enhanced human-type receptor-binding affinity at these markets poses a substantial threat to global public health.

In January, 2024, findings from a surveillance study near Poyang Lake in southern China revealed a high prevalence of novel H5N1 viruses that showed enhanced binding affinity for human-type sialic acid receptors (appendix pp 3–4, 15). These novel H5N1 strains, which share high sequence homology, all harbour D158N and N193K substitutions (H3 numbering) in the receptor-binding site of the hemagglutinin (HA) protein. 

Receptor-binding assays indicated that viruses with the D158 and N193 residues bound exclusively to alpha-2,3-sialylglycopolymers (avian-type receptors), whereas viruses with the N158 and K193 residues acquired the ability to bind to alpha-2,6-sialylglycopolymers (human-type receptors).

Molecular docking experiments suggested that the N193K substitution facilitated a hydrogen bond interaction with the GlcNAc-3 of the human-type receptor, explaining this gain of binding affinity. Although the D158N mutation did not alter the N-glycan pattern at residue 158 (158NDA160), the N193K mutation can be considered a potential marker for binding to human-type receptors.

Phylogenetic analysis showed that these H5N1 viruses are part of the 2·3·4·4b sublineage, which originate from wild bird H5N1 viruses circulating in Japan and South Korea during 2022–23. Furthermore, analysis of polymorphism at residue 193 in the HA protein of H5N1 viruses revealed a variance in prevalence between human and avian hosts. N193 was dominant in avian H5N1 viruses (88·2%), whereas K193 was most prevalent in human isolates (45·1%), with N193 accounting for only 4% of human H5N1 viruses.

Given the established role of LPMs as a major source of human H5N1 infections, we highlight the urgent need for enhanced surveillance and public health interventions to mitigate the widespread transmission potential of these novel human-type receptor-binding H5N1 viruses in these markets.

This research was supported by the National Natural Science Foundation of China (Grant No.32002320), and GuangDong Basic and Applied Basic Research Foundation (Grant No.2024A1515010836). We declare no competing interests.