January 16, 2012 — Worldwide pandemics of influenza caused widespread death and illness in 1918, 1957, 1968 and 2009. A new study examining weather patterns around the time of these pandemics finds that each of them was preceded by La Niña conditions in the equatorial Pacific. The study’s authors–Jeffrey Shaman of Columbia University’s Mailman School of Public Health and Marc Lipsitch of the Harvard School of Public Health—note that the La Niña pattern is known to alter the migratory patterns of birds, which are thought to be a primary reservoir of human influenza. The scientists theorize that altered migration patterns promote the development of dangerous new strains of influenza.
The study findings are published in the journal PNAS.
To examine the relationship between weather patterns and influenza pandemics, the researchers studied records of ocean temperatures in the equatorial Pacific in the fall and winter before the four most recent flu pandemics emerged. They found that all four pandemics were preceded by below-normal sea surface temperatures—consistent with the La Niña phase of the El Niño-Southern Oscillation. This La Niña pattern develops in the tropical Pacific Ocean every two to seven years.
The authors cite other research showing that the La Niña pattern alters the migration, stopover time, fitness and interspecies mixing of migratory birds. These conditions could favor the kind of gene swapping—or genetic reassortment—that creates novel and therefore potentially more infectious variations of the influenza virus.
“We know that pandemics arise from dramatic changes in the influenza genome. Our hypothesis is that La Niña sets the stage for these changes by reshuffling the mixing patterns of migratory birds, which are a major reservoir for influenza,” says Jeffrey Shaman, PhD, Mailman School assistant professor of Environmental Health Sciences and co-author of the study.
Changes in migration not only alter the pattern of contact among bird species, they could also change the ways that birds come into contact with domestic animals like pigs. Gene-swapping between avian and pig influenza viruses was a factor in the 2009 swine flu pandemic.
While a recent paper posited a link between influenza pandemics and strong El Niño events, authors of the current paper note that this 2011 analysis was based on some flawed data. They propose to test the La Niña-influenza theory by studying influenza genetics, avian migration patterns and climate data.
About Columbia University’s Mailman School of Public Health
Founded in 1922 as one of the first three public health academies in the nation, Columbia University’s Mailman School of Public Health pursues an agenda of research, education, and service to address the critical and complex public health issues affecting New Yorkers, the nation and the world. The Mailman School is the third largest recipient of NIH grants among schools of public health. Its over 300 multi-disciplinary faculty members work in more than 100 countries around the world, addressing such issues as preventing infectious and chronic diseases, environmental health, maternal and child health, health policy, climate change & health, and public health preparedness. It is a leader in public health education with over 1,000 graduate students from more than 40 nations pursuing a variety of master’s and doctoral degree programs. The Mailman School is also home to numerous world-renowned research centers including the International Center for AIDS Care and Treatment Programs (ICAP), the National Center for Disaster Preparedness, and the Center for Infection and Immunity. For more information, please visit www.mailman.columbia.edu
Contact: Stephanie Berger, Columbia University’s Mailman School of Public Health, 917-734-8973/212-305-4372, firstname.lastname@example.org