title: The emergence of pandemic influenza viruses.
abstract: Pandemic influenza has posed an increasing threat to public health worldwide in the last decade. In the 20th century, three human pandemic influenza outbreaks occurred in 1918, 1957 and 1968, causing significant mortality. A number of hypotheses have been proposed for the emergence and development of pandemic viruses, including direct introduction into humans from an avian origin and reassortment between avian and previously circulating human viruses, either directly in humans or via an intermediate mammalian host. However, the evolutionary history of the pandemic viruses has been controversial, largely due to the lack of background genetic information and rigorous phylogenetic analyses. The pandemic that emerged in early April 2009 in North America provides a unique opportunity to investigate its emergence and development both in human and animal aspects. Recent genetic analyses of data accumulated through long-term influenza surveillance provided insights into the emergence of this novel pandemic virus. In this review, we summarise the recent literature that describes the evolutionary pathway of the pandemic viruses. We also discuss the implications of these findings on the early detection and control of future pandemics.
authors.affiliation: State Key Laboratory of Emerging Infectious Diseases, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. yguan@hkucc.hku.hk
authors.forename: Yi
authors.initials: Y
authors.lastname: Guan
authors.forename: Dhanasekaran
authors.initials: D
authors.lastname: Vijaykrishna
authors.forename: Justin
authors.initials: J
authors.lastname: Bahl
authors.forename: Huachen
authors.initials: H
authors.lastname: Zhu
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.forename: Gavin J D
authors.initials: GJ
authors.lastname: Smith
mesh_terms: D000818:Animals; D001717:Birds / Q000821:virology; D021821:Communicable Diseases, Emerging / Q000453:epidemiology* / Q000266:history / Q000821:virology*; D019143:Evolution, Molecular; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics*; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics; D005585:Influenza in Birds / Q000453:epidemiology / Q000266:history / Q000821:virology; D007251:Influenza, Human / Q000453:epidemiology* / Q000266:history / Q000821:virology*; D058873:Pandemics / Q000266:history*