Transmission Pathways of Zoonotic Influenza Viruses and Influencing Factors: A Systematic Review of Recent Findings.

Recent outbreaks of zoonotic influenza viruses underscored the need for a deeper understanding of transmission pathways and factors influencing spillover events. Understanding the combined effects of environmental conditions, host interactions, and viral adaptations is essential for effective preparedness and response. The WHO public health research agenda for influenza, revised in 2017, recommended research to further define the host-to-host transmission pathways of influenza type A viruses. Since 2017, important research has been conducted, and the global health landscape has changed. Therefore, there is a need to review the transmission pathway studies conducted during the last eight years. We conducted a systematic analysis following the PRISMA guidelines on 7490 PubMed records from 2017 to 2024, of which 219 records were retained. This review evaluates research on zoonotic influenza virus transmission among wild and domestic animals and cross-species transmission to humans. By examining pathways, host, environmental, and viral factors, this review identified key findings and research gaps. Research remains limited in critical areas including transmission pathways among diverse animals, role of environmental factors, and zoonotic potential across regions. Addressing these gaps is essential for improving public health strategies. This review highlights the necessity of integrating a One Health approach in addressing zoonotic influenza risks.