A G57 (BJ/94-like) H9N2 avian influenza virus exhibits enhanced replication and tissue dissemination in chickens compared with a G1-B virus

Avian influenza H9N2 viruses cause economic losses to the poultry industry and pose a public health risk. Two major H9N2 lineages dominate globally: the G1 lineage (genotype G1-B), prevalent in the Middle East, Africa and South Asia, and the BJ/94 lineage (predominantly genotype G57), dominant in China, Vietnam, South Korea, Indonesia and the Far East. We investigated replication, transmission and pathogenicity of prototype strains from these two lineages to link genotype to phenotype. The G57 virus A/Ck/Vietnam/H7F-14-BN4-315/2014 (Vietnam/315) was more lethal and showed greater tissue dissemination in chicken embryos than the G1-B virus A/chicken/Pakistan/UDL-01/2008 (Pakistan/UDL-01). Vietnam/315 exhibited higher replication in directly infected and contact chickens, with increased oropharyngeal and cloacal shedding and tissue dissemination. In contrast, the Pakistan/UDL-01 virus was …