A widely circulating strain of avian influenza (H9N2) demonstrates significantly greater ability to replicate, spread, and infect chickens compared to another major lineage, research has shown.
Led by The Pirbright Institute, and published in the Journal of General Virology, the study evaluated H9N2 avian influenza viruses common in poultry worldwide, causing economic losses and occasional human infections.
Two dominant lineages currently circulate globally: G1 (common in the Middle East, Africa and Indian subcontinent) and the BJ/94-like lineage (including the G57 genotype), predominantly in East and Southeast Asia.
Scientists compared representative viruses from each lineage: a G57 genotype virus isolated in Vietnam (Vietnam/315) and a G1-B genotype virus isolated in Pakistan (Pakistan/UDL-01).
The researchers found the G57 virus (Vietnam/315) consistently outperformed the G1-B virus across multiple experiments.
Professor Munir Iqbal, Head of Pirbright’s Avian Influenza and Newcastle Disease group, said:
"Our study, which raises concerns for poultry industries and public health, shows the G57 virus replicated more efficiently in chicken embryos and caused significantly higher mortality. Unlike the G1-B virus, which remained largely confined to respiratory tissues, G57 spread throughout multiple organs, including the brain, lungs, and intestines. Chickens infected with the G57 virus shed more virus, both through the respiratory tract and via feces, leading to greater infection of contact birds. And G57 replicated more efficiently in both avian and mammalian cells, indicating stronger overall fitness.”
Supported by funding from UK Research and Innovation’s Biotechnology and Biological Sciences Research Council (BBSRC), the study identified several biological advantages of G57 viruses.
Specific genes, including the matrix (M), PB2, haemagglutinin (HA), and neuraminidase (NA), boost replication and spread. The virus has more active neuraminidase, helping it release from infected cells more efficiently. Its haemagglutinin protein is more acid-stable, potentially aiding survival in the environment and transmission, and the virus shows strong attachment to avian-type receptors, supporting efficient poultry infection.
Professor Iqbal added: “Whilst our study used prototype strains, the findings highlight important differences in how these viruses behave - and why some may pose a greater risk through their ability to exchange genes with other influenza viruses. G57-like viruses have contributed genetic material to other influenza strains known to infect humans, and enhanced replication and shedding increase the chances of spillover from poultry to people. Co-circulation of different strains raises the risk of new, potentially more dangerous variants emerging through genetic reassortment.”
The study underscores the need for continued surveillance of avian influenza viruses, stronger biosecurity measures in poultry production and ongoing monitoring of viral evolution and gene exchange.
Read the Paper: Journal of General Virology – “A G57 (BJ/94-like) H9N2 Avian Influenza Virus Exhibits Enhanced Replication and Tissue Dissemination in Chickens Compared with a G1-B Virus.”