Origin of H1N1 (‘Mexican’ or ‘Swine’ flu)

The accompanying graph reveals the origin of the ‘Swine flu virus’ as deduced from sequence analysis of the respective genome segments, that through a process of so-called “re-assortment” shaped the new virus. All the eight segments originate from avian influenza A viruses that were introduced into pigs directly from birds or through a human intermediate host. The colour codes correspond with those of the parent viruses. Where and in which species the final reassortment has taken place has not been fully elucidated.