New England Journal of Medicine
Volume 361 — July 16, 2009 — Number 3
http://content.nejm.org/current.shtml

Review Article
Current Concepts: Historical Perspective — Emergence of Influenza A (H1N1) Viruses
S. M. Zimmer and D. S. Burke

[First 100 words and section headings per NEJM convention]
On April 17, 2009, officials at the Centers for Disease Control and Prevention (CDC) confirmed two cases of swine influenza in children living in neighboring counties in California.1 Here we take a perspective from systems biology to review the series of evolutionary and epidemiologic events, starting in 1918, that led to the emergence of the current swine-origin influenza A (H1N1) strain (S-OIV), which is widely known as swine flu. This article is one of two historical articles on influenza A (H1N1) viruses in this issue of the Journal. Our review focuses on the key steps that characterize this viral…

– Emergence of a Virus

– Simultaneous Appearance in Humans and Swine (1918)

– Antigenic Divergence of Human and Swine Influenza (1918–1930)

– Evolution of the 1918 Virus in Humans (1918–Present)

– Intrasubtypic Reassortment of Human H1N1 Virus (1947)

– Extinction of Human H1N1 Virus (1957)

– Sporadic Cross-Species Transfers (1958–Present)

– H1N1 Reemergence in Humans (1977)

– Seasonal Influenza A (H1N1) (1977–Present)

– Emergence of New H1N1 Strains in Swine (1979–Present)

– Sporadic Cross-Species Transmission of Triple Reassortant Virus (1998–2009)

– Reassortment of Two H1 Swine Viruses (2008–2009)

– Competition between Seasonal and Newly Emerged Viruses