Interspecies Transmission of Influenza A Viruses Between Swine and Poultry

The special susceptibility of pigs to infection with avian and mammalian influenza viruses, the close proximity of pigs and poultry farms, and applied human practices in raising and trading of farm animals/farm animal products, provide opportunities for genetic exchange and interspecies transmission of influenza A viruses. Although only H1 and H3 influenza subtypes have widely circulated and caused disease in pig populations worldwide, H9 subtype is being continuously detected in pigs in Asia, plus sporadic infections with highly pathogenic H5-avian influenza viruses. On the other hand, swine viruses are continuously isolated from poultry species, especially turkeys, causing economic losses in poultry production. The viral and host factors contributing to influenza transmission between pigs and poultry are poorly defined. In addition, surveillance programs for influenza viruses in both species, especially pigs, are rarely implemented, and thus, leaving many questions about influenza unanswered. In this review, we summarize early and recent findings about influenza transmission between swine and poultry with emphasis on the role of turkeys.