Preplanned Studies: #Phylogenetic and #Molecular Characteristics of An #H3N8 Avian #Influenza Virus Detected in Wild #Birds — #Beijing, #China, September 2024

 

Summary

-- What is already known about this topic?

- The H3N8 avian influenza virus (AIV) demonstrates considerable capacity for interspecies transmission and has been documented in multiple mammalian hosts, including equine and canine species. During 2022–2023, three laboratory-confirmed human infections with H3N8 were reported in China, heightening public health concerns about the zoonotic spillover potential of H3 subtype AIVs.

-- What is added by this report?

- This study reports the isolation of a genetically reassorted, low-pathogenicity H3N8 avian influenza virus (AIV) from an islet in Niukouyu Wetland Park, Beijing Municipality — the first detection of this viral strain in a wild environment within the city. Throat swabs collected from park staff tested negative for influenza viruses. Phylogenetic analysis demonstrated that the viral hemagglutinin gene originated from the Eurasian lineage, while the neuraminidase gene was derived from the North American lineage. Although no direct evidence of human infection has been documented, multiple mutations identified in the virus’s internal genes are associated with enhanced replication capacity, increased virulence, and improved adaptation to mammalian hosts. These molecular features indicate a potential risk for cross-species transmission to humans.

-- What are the implications for public health practice?

- Given the potential threat that H3N8 AIVs pose to mammalian species, including humans, this study emphasizes the critical need to strengthen influenza surveillance networks and broaden monitoring efforts specifically targeting H3 subtype AIVs.

ABSTRACT

Introduction: 

The H3N8 avian influenza virus (AIV) is recognized for its capacity for interspecies transmission and has been detected in multiple mammalian hosts. Between 2022 and 2023, three human infections with H3N8 were documented in China, raising significant concerns about its zoonotic spillover potential. In this study, we characterized an H3N8 isolate from Niukouyu Wetland Park in Beijing Municipality to elucidate the genetic variability and evolutionary dynamics of this AIV subtype.

Methods: 

The virus underwent whole-genome sequencing followed by comprehensive molecular and phylogenetic characterization.

Results: 

We identified a genetically reassorted, low-pathogenicity H3N8 AIV, marking the first detection of this subtype in a wild environment in Beijing. Throat swabs from the park staff tested negative for influenza viruses. Phylogenetic analyses demonstrated that the viral hemagglutinin and neuraminidase genes originated from Eurasian and North American lineages, respectively. Nucleotide sequence comparisons revealed 97.57%–99.06% similarity between the eight gene segments of this virus and those of reference strains. Multiple internal gene mutations were identified, including PB2-K318R and PB1-F2-N66S, which are associated with enhanced polymerase activity, increased virulence, and improved mammalian adaptation.

Conclusions: 

The molecular characteristics of this H3N8 virus indicate a potential risk for cross-species transmission to humans, emphasizing the critical need to strengthen influenza surveillance networks and expand monitoring efforts targeting H3 subtype AIVs.

Source: China Centre for Disease Control and Prevention, Weekly Update, https://weekly.chinacdc.cn/en/article/doi/10.46234/ccdcw2025.233

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