Phylogenetic and Phylogeographic Analysis of the Highly Pathogenic H5N6 Avian Influenza Virus in China

Recombinant duck enteritis virus bearing the hemagglutinin genes of H5 and H7 influenza viruses is an ideal multivalent live vaccine in ducks

Due to the fact that many avian influenza viruses that kill chickens are not lethal to ducks, farmers are reluctant to use avian influenza inactivated vaccines on ducks. Large numbers of unvaccinated ducks play an important role in the transmission of avian influenza viruses from wild birds to domestic poultry, creating a substantial challenge to vaccination strategies for avian influenza control. To solve this problem, we constructed a recombinant duck enteritis virus (DEV), rDEV-dH5/H7, using a live attenuated DEV vaccine strain (vDEV) as a vector. rDEV-dH5/H7 carries the hemagglutinin gene of two H5 viruses [GZ/S4184/17 (H5N6) (clade 2.3.4.4 h) and LN/SD007/17 (H5N1) (clade 2.3.2.1d)] and an H7 virus [GX/SD098/17 (H7N9)]. These three hemagglutinin genes were stably inherited in rDEV-dH5/H7 and expressed in rDEV-dH5/H7-infected cells. Animal studies revealed that rDEV-dH5/H7 and vDEV induced similar neutralizing antibody responses and protection against lethal DEV challenge. Importantly, rDEV-dH5/H7 induced strong and long-lasting hemagglutinin inhibition antibodies against different H5 and H7 viruses and provided complete protection against challenges with homologous and heterologous highly pathogenic H5 and H7 influenza viruses in ducks. Our study shows that rDEV-dH5/H7 could serve as an ideal live attenuated vaccine to protect ducks against infection with lethal DEV and highly pathogenic avian influenza viruses.

Investigating the Genetic Diversity of H5 Avian Influenza Viruses in the United Kingdom from 2020-2022

Since 2020, the United Kingdom and Europe have experienced annual epizootics of high-pathogenicity avian influenza virus (HPAIV). The first epizootic, during the autumn/winter of 2020-2021, involved six H5Nx subtypes, although H5N8 HPAIV dominated in the United Kingdom. While genetic assessments of the H5N8 HPAIVs within the United Kingdom demonstrated relative homogeneity, there was a background of other genotypes circulating at a lower degree with different neuraminidase and internal genes.  Following a small number of detections of H5N1 in wild birds over the summer of 2021, the autumn/winter of 2021-2022 saw another European H5 HPAIV epizootic that dwarfed the prior epizootic. This second epizootic was dominated almost exclusively by H5N1 HPAIV, although six distinct genotypes were defined. We have used genetic analysis to evaluate the emergence of different genotypes and proposed reassortment events that have been observed. The existing data suggest that the H5N1 viruses circulating in Europe during late 2020 continued to circulate in wild birds throughout 2021, with minimal adaptation, but then went on to reassort with AIVs in the wild bird population. We have undertaken an in-depth genetic assessment of H5 HPAIVs detected in the United Kingdom over two winter seasons and demonstrate the utility of in-depth genetic analyses in defining the diversity of H5 HPAIVs circulating in avian species, the potential for zoonotic risk, and whether incidents of lateral spread can be defined over independent incursions of infections from wild birds. This provides key supporting data for mitigation activities. IMPORTANCE High-pathogenicity avian influenza virus (HPAIV) outbreaks devastate avian species across all sectors, having both economic and ecological impacts through mortalities in poultry and wild birds, respectively. These viruses can also represent a significant zoonotic risk. Since 2020, the United Kingdom has experienced two successive outbreaks of H5 HPAIV. While H5N8 HPAIV was predominant during the 2020-2021 outbreak, other H5 subtypes were also detected. The following year, there was a shift in the subtype dominance to H5N1 HPAIV, but multiple H5N1 genotypes were detected. Through the thorough utilization of whole-genome sequencing, it was possible to track and characterize the genetic evolution of these H5 HPAIVs in United Kingdom poultry and wild birds. This enabled us to assess the risk posed by these viruses at the poultry-wild bird and the avian-human interfaces and to investigate the potential lateral spread between infected premises, a key factor in understanding the threat to the commercial sector.

Pathogenicity and Transmissibility of Clade 2.3.4.4h H5N6 Avian Influenza Viruses in Mammals

Avian influenza viruses (AIVs) have the potential for cross-species transmission and pandemics. In recent years, clade 2.3.4.4 H5N6 AIVs are prevalent in domestic poultry, posing a threat to the domestic poultry industry and public health. In this study, two strains of H5N6 AIVs were isolated from chickens in Hebei, China, in 2019: A/chicken/Hebei/HB1907/2019(H5N6) and A/chicken/Hebei/HB1905/2019(H5N6). Phylogenetic analysis showed that both viral HA genes clustered in the 2.3.4.4h clade. Receptor binding analysis showed that the HB1905 strain preferentially binds to α-2,3-linked sialic acid (SA) receptors, while the HB1907 strain preferentially binds to α-2,3- and α-2,6-linked sialic acid (SA) receptors. During early infection, the HB1907 strain is highly replicable in MDCK cells, more so than the HB1905 strain. Pathogenicity assays in mice showed that both viruses could replicate in the lungs without prior adaptation, with HB1907 being more highly pathogenic in mice than the HB1905 strain. Significantly, both the HB1905 and HB1907 strains can be transmitted through direct contact among guinea pigs, but the transmission efficiency of the HB1907 strain through contact between guinea pigs is much greater than that of the HB1905 strain. These results strengthen the need for ongoing surveillance and early warning of H5N6 AIVs in poultry.

Pathogenicity and Transmissibility of Goose-Origin H5N6 Avian Influenza Virus Clade 2.3.4.4h in Mammals

Throughout the last decade, H5N6 avian influenza viruses (AIVs) circulating in poultry and infecting humans have caused increasing global concerns that they might become a pandemic threat to global health. Since AIVs could occasionally cause asymptomatic infections in geese, virus monitoring in such a host should be critical to the control of cross-species infection. In addition, previous studies showed that clade 2.3.4.4h H5N6 AIVs could infect mammals without adaptation. However, the pathogenicity and transmissibility of goose-origin clade 2.3.4.4h H5N6 AIVs in mammals remain unknown. In this study, two H5N6 AIVs were isolated from a domestic chicken (A/chicken/Hebei CK05/2019 (H5N6)) and a goose (A/goose/Hebei/GD07/2019(H5N6)). This study is the first to evaluate the pathogenicity and transmissibility of goose-origin clade 2.3.4.4h H5N6 AIVs in mammals by comparison with chicken-origin 2.3.4.4h H5N6 AIVs. The CK05 virus had an affinity for α-2,3-receptors, while the GD07 virus had an affinity for both α-2,3-and α-2,6-receptors. The GD07 virus had a higher replication capacity in vitro and more severe pathogenicity in mice than the CK05 virus. The CK05 virus could not be transmitted effectively among guinea pigs, whereas the GD07 virus could be transmitted through direct contact among guinea pigs. The results of this study indicated the potential health threat of clade 2.3.4.4h H5N6 AIVs to mammals and emphasized the importance of continuous monitoring of H5N6 AIVs, especially in waterfowl.