Pigs as ‘Mixing Vessels’ for the Creation of New Pandemic Influenza A Viruses

Human influenza A viruses do not spread in the bird population and vice versa. The viral component involved in keeping influenza A viruses of these two independently evolving reservoirs apart is the nucleoprotein. However, reassortants with a mixed genome are created through antigenic shift. This kind of recombination between avian and human influenza A strains seems to occur during double infection, specifically of pigs which are tolerant of becoming infected with influenza A viruses from both reservoirs. To minimize the probability of such antigenic shift, it is recommended that pigs are kept in closed farms, especially in southeast Asia, the starting point of most influenza pandemics.