Continuing evolution of H6N2 influenza a virus in South African chickens and the implications for diagnosis and control

Abstract

BackgroundThe threat of poultry-origin H6 avian influenza viruses to human health emphasizes the importance of monitoring their evolution. South Africa’s H6N2 epidemic in chickens began in 2001 and two co-circulating antigenic sub-lineages of H6N2 could be distinguished from the outset. The true incidence and prevalence of H6N2 in the country has been difficult to determine, partly due to the continued use of an inactivated whole virus H6N2 vaccine and the inability to distinguish vaccinated from non-vaccinated birds on serology tests. In the present study, the complete genomes of 12 H6N2 viruses isolated from various farming systems between September 2015 and February 2019 in three major chicken-producing regions were analysed and a serological experiment was used to demonstrate the effects of antigenic mismatch in diagnostic tests.ResultsGenetic drift in H6N2 continued and antigenic diversity in sub-lineage I is increasing; no sub-lineage II viruses were detected. Reassortment patterns indicated epidemiological connections between provinces as well as different farming systems, but there was no reassortment with wild bird or ostrich influenza viruses. The sequence mismatch between the official antigens used for routine hemagglutination inhibition (HI) testing and circulating field strains has increased steadily, and we demonstrated that H6N2 field infections are likely to be missed. More concerning, sub-lineage I H6N2 viruses acquired three of the nine HA mutations associated with human receptor-binding preference (A13S, V187D and A193N) since 2002. Most sub-lineage I viruses isolated since 2015 acquired the K702R mutation in PB2 associated with the ability to infect humans, whereas prior to 2015 most viruses in sub-lineages I and II contained the avian lysine marker. All strains had an unusual HA0 motif of PQVETRGIF or PQVGTRGIF.ConclusionsThe H6N2 viruses in South African chickens are mutating and reassorting amongst themselves but have remained a genetically pure lineage since they emerged more than 18 years ago. Greater efforts must be made by government and industry in the continuous isolation and characterization of field strains for use as HI antigens, new vaccine seed strains and to monitor the zoonotic threat of H6N2 viruses.

Molecular Characterization and Pathogenesis of H6N6 Low Pathogenic Avian Influenza Viruses Isolated from Mallard Ducks (Anas platyrhynchos) in South Korea

“…Generally, H6 isolates receptor-binding sites were composed of HA protein residues (Q226 and G228), which preferentially bind to the α-2,3-linked sialic acid receptors in avian bird species [ 61 ]. Similarly, based on previous reports, the following HA protein residues: A137N, P186L, A193N, and G228S, were associated with human receptor-binding preference and were not found in our H6N6 isolate [ 7 , 15 ]. Furthermore, H6N6 isolates can be modified to replace V187D in HA responses for the binding affinity might be adapted to mammalian receptors [ 66 ].…”

“…Downie and Laver reported in 1973 that the H6 subtype AIVs were isolated in 1965 in Massachusetts in the United States [ 6 ]. Following this discovery, the H6 subtype of AIVs has been frequently identified in isolates obtained from poultry birds, wild birds, and domestic birds around the world [ 7 ]. Over the past two decades, surveillance studies indicate that H6 subtypes have become enzootic in wild birds of southern China, mostly as H6N6 isolates.…”

Evolution and pathogenicity of H6 avian influenza viruses isolated from Southern China during 2011 to 2017 in mice and chickens

“…The receptor-binding sites in the viral HA proteins possess the residues Q226 and G228, similar to those H6 isolates reported previously, which preferentially bind to the α-2,3-linked sialic acid receptors predominant in avian species 45,46 . However, the E190V and N192D substitutions of H6 HA have been associated with interspecies transmission of AIVs from ducks to chickens 47 , but those amino acids were not found in the five H6 AIVs (GD/1127/H6N2, GD/E3503/H6N2, HN/A729/H6N6, ZJ/B2028/H6N6 and FJ/D3480/H6N6) in this study, which would be the most likely reason that the replication of the H6 isolates in chickens was surprisingly limited. The residues 228S, 137N, 186L, A13S, and A193N at HA associated with human receptor-binding preference 45,47 were not found in H6 isolates in this study.…”

“…However, the E190V and N192D substitutions of H6 HA have been associated with interspecies transmission of AIVs from ducks to chickens 47 , but those amino acids were not found in the five H6 AIVs (GD/1127/H6N2, GD/E3503/H6N2, HN/A729/H6N6, ZJ/B2028/H6N6 and FJ/D3480/H6N6) in this study, which would be the most likely reason that the replication of the H6 isolates in chickens was surprisingly limited. The residues 228S, 137N, 186L, A13S, and A193N at HA associated with human receptor-binding preference 45,47 were not found in H6 isolates in this study. Additionally, almost all H6N6 isolates have the substitution of HA at V187D, the binding affinity might be altered to adapt to mammalian receptors 19 .…”

Dose immunogenicity study of a plant-produced influenza virus-like particle vaccine in layer hens

“…Avian influenza, which is caused by various subtypes of Influenza A virus (IAV), poses one of the largest known threats to global poultry production as well as human health [ 1 ]. Most developed countries are well-resourced to detect and control outbreaks of avian influenza early, opting to eradicate the virus in poultry through strict biosecurity with mass culling, but in other regions, subtype H9N2 [ 2 ], H6N2 [ 3 , 4 ], H5Nx or H7Nx low pathogenic (LPAI) or high pathogenic (HPAI) strains spread too rapidly and widely to eradicate and eventually became enzootic [ 5 , 6 , 7 , 8 ], leaving vaccination as the only option to keep poultry production economically viable and assure food security. However, poor vaccines or poorly-applied vaccines have little effect on controlling disease or reducing virus spread, and can even potentiate the emergence of undesirable variant viruses [ 3 , 9 ].…”