@@ Influenza A viruses can infect a variety of animals, there are a limited numbers of host-specific influenza A viruses,i.e., humans (H1N1, H3N2, H2N2, and H1N2), pigs (H1N1, H3N2 and H1N2), horses (H3N8 and H7N7), dogs (H3NS),and domestic avian species (H5N1, H5N2, H7N7, and HgN2). Generally, because of long time independent evolution of host specific viruses, it is not easy that individual viruses cross interspecies barrier to infect another new host. Pigs are susceptible to both avian and human viruses because their tracheal epithelium possess both kinds of receptor, so pigs have been postulated to serve as mixing vessels for the generation of human, avian, and/or swine reassortant viruses with potential to cause a pandemic in human, which exemplified by 2009 pandemic NH1N1 viruses through reassortment of swine-origin viruses. Influenza virus infection is an important febdle respiratory disease in pigs. Swine influenza viruses are enzootic among pigs worldwide. Currently, three predominant subtypes of influenza virus are