A comprehensive new research study has revealed alarming genetic changes in H9N2 avian influenza viruses found in Chinese poultry, shedding light on why this strain poses an escalating threat to human health.
By Maile Matsimela, Digital Editor at African Farming
The research, detailed in Nature Microbiology, demonstrates extensive genetic and antigenic variation among H9N2 strains currently spreading through China’s poultry populations – variations that may explain the virus’s persistent circulation despite active vaccination programmes.
Three Decades of Evolution
H9N2 avian influenza was first detected in China in 1994 and has since become the predominant strain affecting poultry. Despite continued vaccination efforts, the virus has not only persisted but has also shown an increasing ability to infect humans, raising significant public health concerns.
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The research team, led by Prof. Bi Yuhai and Prof. George F. Gao from the Chinese Academy of Sciences’ Institute of Microbiology, along with Prof. Shi Weifeng from Shanghai Jiao Tong University’s Ruijin Hospital, conducted an extensive analysis of the virus’s genetic evolution and its capacity for cross-species transmission.
Surveillance Reveals Dominant Lineage
Through the Center for Influenza Research and Early-warning (CASCIRE), researchers have maintained continuous monitoring of avian influenza viruses since 2014. Their surveillance of live poultry markets between 2019 and 2023 showed that the A/chicken/Beijing/1/94 (BJ94) lineage remains the dominant H9N2 variant in poultry.
To track the virus’s evolution more effectively, the team created an innovative classification system for BJ94 viruses and launched an online platform allowing researchers worldwide to monitor H9 virus development.
Multiple Strains, Multiple Threats
The researchers identified 10 different hemagglutinin (HA) sub-subclades currently circulating in poultry populations, each displaying unique antigenic characteristics. This diversity may explain why current vaccination strategies have failed to control the H9N2 epidemic effectively.
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Dangerous Mutations on the Rise
Perhaps most concerning, the study found increasing prevalence of specific mutations linked to enhanced infectivity and pathogenicity in mammals:
- 99.46% of H9N2 samples from 2021-2023 carried the HA-L226 mutation, which enables binding to human receptors;
- 96.17% contained the NP-N52 mutation, providing resistance to human MxA antiviral proteins; and
- 32.61% had the PB2-V627 mutation, which boosts polymerase activity in human cells.
Laboratory testing confirmed that viruses with these mutations showed preferential binding to human-type receptors, replicated effectively in human cells, and demonstrated the ability to transmit through both direct contact and airborne particles in animal models – all indicators of significant zoonotic potential.
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Implications for Public Health
The findings underscore the urgent need for improved surveillance systems, updated vaccination approaches and enhanced understanding of avian influenza evolution to address the mounting H9N2 threat to human health.
The research received funding from China’s National Key R&D Program and the National Natural Science Foundation of China for Distinguished Young Scholars.
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