From Surfaces to Spillover: Environmental Persistence and Indirect Transmission of Influenza A(H3N8) Virus

Avian influenza viruses (AIVs) pose a significant zoonotic threat, with the emerging H3N8 subtype raising increasing concern due to sporadic human infections. Current strategies for risk assessment of novel AIVs primarily rely on genetic surveillance and isolated case reports, which provide limited insight into their cross-species transmission potential. However, these approaches may overlook critical phenotypic determinants, such as pathogenicity, transmissibility, and environmental persistence, that directly influence zoonotic risk. This study investigates the evolutionary relationships, receptor-binding properties, replication dynamics, pathogenicity in mice, transmission efficiency in guinea pigs, and environmental persistence of three H3N8 strains isolated from a live poultry market. All three H3N8 strains bound exclusively to α-2,3 sialic acid receptor and achieved 100% transmissibility among guinea pigs through direct contact. Notably, the environment-origin strain A09 exhibited an indirect contact transmission efficiency of 33.3%. The findings reveal strain-specific differences, with A09 displaying enhanced pathogenicity, broader transmission routes, and greater environmental persistence compared with A05 and A01. This perspective underscores the value of integrated profiling from genotype to phenotype combined with multi-route transmission and environmental persistence analyses to delineate the adaptive roadmap of H3N8 from avian to mammalian hosts and to assess its emerging infection risk. Future directions for surveillance and intervention were also discussed, highlighting their potential to strengthen preparedness against zoonotic influenza threats.