Reassortment Patterns in Swine Influenza Viruses

Previous human influenza pandemics were the results of emerging viruses from non-human reservoirs, with at least two caused by strains of mixed human and avian origin. Also, many cases of swine influenza viruses have reportedly infected humans, including the recent human H1N1 strain, isolated in Mexico and the United States. Pigs are documented to get infected with human, avian, and swine viruses and allow productive replication, thus it has been conjectured that they are the "mixing vessel" that create reassortant strains, causing the human pandemics. In this paper, we apply several statistical techniques to an ensemble of publicly available swine viruses to study the reassortment phenomena. The reassortment patterns in swine viruses confirm previous results found in human viruses that the glycoprotein coding segments reassort most often. Moreover, one of the polymerase segments (PB1), reassorted in the strains responsible for the last two human pandemics of 1957 and 1968, also reassorts frequently.