# 6078
We have an interesting hypothesis being offered today by a pair of well-respected researchers (Jeffrey Shaman of Columbia University's Mailman School of Public Health and Marc Lipsitch of the Harvard School of Public Health), who note that the weather patterns prior to the pandemics of 1918, 1957, 1968 and 2009 all showed the Pacific ocean to be in a La Niña cycle.
We know, of course, that correlation doesn’t necessarily imply causation, but an apparent association between two events can often provide a useful starting point for further scientific investigation.
And that’s what these researchers are calling for.
Whether this correlation is casual, or is simply coincidental, is for now unknown.
For those unfamiliar with the basics of El Niño and La Niña, a very brief overview:
The Pacific Ocean cycles between an El Niño pattern (warmer) and a La Niña (colder) than normal water temperatures in the Equatorial Pacific Ocean.
These water temperature cycles can have major effects on climate and weather far removed from the Pacific. During La Niña years, for example, the Atlantic Hurricane season is usually more active.
La Niña (December 2000)
El Niño (December 1997)
Sea surface temperature anomalies (°C)Photo Credit- NOAA
La Niña's occur every 2 to 7 years, and over the past 62 years 14 have been observed. During that time, we saw 3 pandemics (1957, 1968, 2009).
Graph Credit- Wikipedia
We’ve the Press Release from Columbia University's Mailman School of Public Health, but after a quick visit to the PNAS journal website I wasn’t able to locate the article online. I imagine it will be online shortly.
Does the La Niña weather pattern lead to flu pandemics?
Public release date: 16-Jan-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 currently published online in 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 and seven years approximately.
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 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.
For the record, the Pacific is currently in a La Niña cycle, and the forecast is for it to remain so well into the Northern Hemisphere spring of 2012.
This is an interesting hypothesis, and should promote some fascinating avenues of investigation.
