Figure 5. A transmission model illustrating the mechanisms of H7 IAV transmission and evolution between wild waterbirds and domestic poultry.

An H7 IAV capable of binding to sialic acid receptors containing either Neu5Gc or Neu5Ac can be transmitted among wild waterbirds possessing these receptors, and can also transit between wild and domestic waterbirds expressed with the same receptors. This virus may then spill over into domestic poultry species (or another wild bird species) that expresses only Neu5Gc. Subsequent to this, the virus could acquire adaptive amino acid substitutions in the HA protein, leading it to lose its Neu5Gc binding ability and exclusively bind to Neu5Ac. Consequently, the transmission capability of these adapted viruses in waterbirds decreases.