In a recent study published within the Emerging Infectious Diseases Journal, researchers investigated the genetic origin, distribution patterns, and antigenicity of two deceased migrating swans from China infected with the H5N1 novel avian influenza viruses (AIVs).
Study: Novel Avian Influenza Virus (H5N1) Clade 2.3.4.4b Reassortants in Migratory Birds, China. Image Credit: KaterynaKon/Shutterstock.com
Background
Highly pathogenic AIVs (HPAIVs) akin to H5N1 were discovered in 1996, and ever since, H5-type HPAIV species have developed into antigenically divergent genetic clades, leading to persistent outbreaks amongst birds.
Long-distance and rapid transmission of H5-type HPAIVs indicates that migratory birds are crucial to HPAIV transmission across the globe.
So far, at the least 4 waves of H5 virus transmission have occurred: 2.2 clade H5N1 viruses between 2005 and 2006, H5N1 2.3.2.1c clade H5N1 viruses between 2009 and 2010, 2.3.4.4a clade H5N8 clade and a pair of.3.2.1c clade H5N1 viruses between 2014 and 2015, and a pair of.3.4.4b clade H5Ny viruses between 2016 and 2017.
Essentially the most recent outbreak of two.3.4.4b clade H5N1/H5N8 HPAIV epidemics amongst wild and domesticated birds in Africa and Eurasia commenced in 2020-2021.
H5N1, H5N6, and H5N8 infections have been infrequently reported amongst humans, emphasizing the potential for zoonotic transmission of H5 highly pathogenic AIVs.
H5 HPAIVs were accountable for a minimum of nine outbreaks amongst wild avian species on the Chinese mainland since 2021. Major H5N1 HPAIV outbreaks in domesticated poultry occurred in the US (US) and Europe between 2021 and 2022.
Concerning the study
In the current study, researchers reported on H5N1 clade 2.3.4.4b reassortment among the many migrating avian population of China.
Oral swabs and pulmonary samples were obtained from a dead whooper in Inner Mongolia, North China, and a dead black-colored swan in Zhejiang, East China, on 3 November and 15 November 2021, respectively.
Subsequently, viruses were isolated amongst specific pathogen-free (SPF) chicken embryos and verified using reverse transcription polymerase chain response (RT-PCR).
Sanger sequencing was performed, and the entire genomes were deposited within the Global Initiative on Sharing All Influenza Data (GISAID) and NMDC databases.
The team reconstructed Bayesian time-resolved phylogenetic origin trees for all three H5N1 viral isolate genes based on the National Centre for Biotechnology Information (NCBI) and GISAID references.
Further, geographic evaluation was performed to map the spatial coordinates. As well as, the team mapped the host types and neuraminidase (NA) or hemagglutinin (HA) subtypes to determine essentially the most probable avian virus ancestor.
Moreover, hemagglutination inhibition (HI) assays were performed to evaluate Re-11 [H5N6 (A/duck/Guizhou/S4184/2017)], Re-13 [H5N6 (A/duck/Fujian/S1424/2020)], and the Re-14 [H5N8 (A/whooper swan/Shanxi/4–1/2020)] vaccine immunogenicity against the H5N1 viruses and H5N8 HPAIVs, which were detected within the 12 months 2020.
Results
In November 2021, three H5N1 HPAIVs were detected, i.e., the Ws/NC/AK1-O/2021 virus and the Ws/NC/AK2-O/2021 virus amongst samples from the dead whooper of North China, and the Bs/EC/74-Lg/2021 virus from those of the deceased black swan of East China.
The H5N1 strains induced severe histopathologic alterations amongst wild avian species, characteristic of HPAIVs, including quite a few basic-type amino acid molecules at the location of HA breakdown.
All three H5N1 HA genes shared the two.3.4.4b.2 clade. Phylogenetic evaluation showed that the three recent H5N1 viral strains were reassortants from Ws/2021 (Ws/NC/AK1-O/2021 and Ws/NC/AK2-O/2021) and Bs/2021 (Bs/EC/74-Lg/2021).
Several regrouping activities amongst H5N8 HPAIVs produced the viruses. The ancestors of most genes within the two reassortants originated from wild Anseriformes and were most likely transmitted during summer 2021, aside from genes akin to the Bs/2021-like M gene, which might need evolved from domesticated poultry.
Nearly all neuraminidase genes of the H5N1 viruses discovered on China’s mainland between 1996 and 2018 were of the EA-1 clade. The primary cluster included 4 H5N8 HPAIVs discovered amongst wild avian species in 2020, the Re-14 strain, eight H5N6 viruses, and one H5N8 virus that caused human infections.
Bs/EC/74-Lg/2021 clustered with H5N1 influenza viruses originating from South Korea and Japan within the second cluster, with 99.0% to 100.0% similar sequences.
Within the third cluster, the North China whooper swan-derived viruses showed 99.0% antigenic similarity and grouped with European-origin H5N1 viral strains. Most H5N1 viruses discovered between 2020 and 2021 were grouped within the third cluster.
Moreover, two H5N1 (third cluster) virus infections were documented amongst United Kingdom (UK) and US residents between 2021 and 2022.
The HA evaluation showed antibody titers 256 between homolog antisera and H5 vaccine antigens and far lower titers (2.0 to 16) for Re-11 and Re-13 by contemporary H5N1/H5N8 viruses.
As compared, H5N8 viruses from the primary cluster showed modest antibody titers (64.0) for the Re-14 antiserum. Ws/NC/AK1-O/2021 and Bs/EC/74-Lg/2021 H5N1 viruses from the second and third clusters, respectively, exhibited titers of 32 and 128, respectively.
Conclusion
Overall, the study findings highlighted the detection of three H5N1 HPAIVs amongst wild avian species throughout the fall of 2021 in China that underwent reassortment during long-distance transmission via avian migratory routes.
The low antigenic similarity amongst H5N1 and H5N8 viruses, despite originating from the identical genetic clade, underscores elevated risks of H5N1 infections amongst inadequately protected flocks within the Chinese mainland.
The findings also highlighted the necessity for globally coordinated AIV monitoring amongst migratory birds to facilitate early detection and prompt treatment of AIV infections.