"aquatic birds are known to serve as the source of all influenza viruses for other species (1
). despite their common origin, influenza a viruses generally are restricted in host range. the host range restriction is a polygenic trait, and the receptor specificity of hemagglutinin (ha) is considered an important determinant (7
). the tracheal epithelium in pigs expresses receptors for both human and avian influenza viruses, and this provides a biological basis for the susceptibility of pigs to both avian and human influenza viruses (8
). pigs, therefore, can function as intermediate hosts, or mixing vessels, in establishing new influenza virus lineages by supporting coinfection, replication, and reassortment among human, avian, and swine influenza viruses (1
and that, in a nutshell, is species-to-species jumps explained.
thanks for that link. fascinating, what i just learned.