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The El Ni?o–Southern Oscillation (ENSO)–pandemic Influenza connection: Coincident or causal?

  1. Marc Lipsitchb
  1. aDepartment of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, NY 10032; and
  2. bCenter for Communicable Disease Dynamics, Harvard School of Public Health, Harvard University, Boston, MA 02115
  1. Edited by Rita R. Colwell, University of Maryland, College Park, MD, and approved September 19, 2011 (received for review May 26, 2011)

Abstract

We find that the four most recent human influenza pandemics (1918, 1957, 1968, and 2009), all of which were first identified in boreal spring or summer, were preceded by La Ni?a conditions in the equatorial Pacific. Changes in the phase of the El Ni?o–Southern Oscillation have been shown to alter the migration, stopover time, fitness, and interspecies mixing of migratory birds, and consequently, likely affect their mixing with domestic animals. We hypothesize that La Ni?a conditions bring divergent influenza subtypes together in some parts of the world and favor the reassortment of influenza through simultaneous multiple infection of individual hosts and the generation of novel pandemic strains. We propose approaches to test this hypothesis using influenza population genetics, virus prevalence in various host species, and avian migration patterns.

Footnotes

  • ?1To whom correspondence should be addressed. E-mail: jls106{at}columbia.edu.
  • Author contributions: J.S. designed research; J.S. performed research; J.S. and M.L. analyzed data; and J.S. and M.L. wrote the paper.

  • Conflict of interest statement: M.L. discloses consulting or honorarium income from the Avian/Pandemic Flu Registry (Outcome Sciences; funded in part by Roche), AIR Worldwide, Pfizer, and Novartis.

  • This paper results from the Arthur M. Sackler Colloquium of the National Academy of Sciences, “Fostering Advances in Interdisciplinary Climate Science” held March 31–April 2, 2011, at the AAAS Auditorium in Washington, DC. The complete program and audio files of most presentations are available on the NAS Web site at www.nasonline.org/climate-science.html.

  • This article is a PNAS Direct Submission.

Online Impact

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