A shifting global climate pattern could portend a flu pandemic, and possibly an opportunity to stop the virus early, a study suggests.
The link, according to researchers, is weather's influence on the migratory patterns of wild birds, the primary pool for human flu.
"Changes in flight patterns -- length, stopovers -- can bring together bird species that otherwise wouldn't intermingle," said Jeffrey Shaman, an environmental health scientist at the Mailman School of Public Health at Columbia University, lead researcher of the preliminary study.
And while mixing with feathered strangers, particularly on water, birds can share viruses orally and fecally. Multiple versions of the flu may then enter a bird's cells, genetically mingling into a "radically different" viral strain "to which the human population has never been exposed," and are therefore susceptible, Shaman explained.
"That's what seeds a pandemic," Shaman told The Huffington Post. Other animals and their viruses may also participate in the pool party. The virus behind the 2009 swine flu pandemic, for example, was a mixture of genetic material from human, bird and pig flu.
In the study, published Monday in the Proceedings of the National Academy of Sciences, Shaman and his colleague, Marc Lipsitch of the Harvard School of Public Health, found that the last four major flu pandemics -- in 1918, 1957, 1968 and 2009 -- all followed a climate pattern called La Nina, which brings colder-than-normal sea surface temperatures in the central Pacific Ocean and generally results in cooler global temperatures. One of these episodes, which occur every two to seven years, is currently underway.
If the theory holds, it could provide "a little lead time" to prepare for what have generally been unpredictable pandemics, said Shaman. "It could allow us to intensify our vigilance and put more resources in place."
Shaman and other experts emphasized that it's too early to rule out the possibility of a coincidence. He also cautions against overreacting to the potential viral consequences of this year's La Nina. In fact, most La Ninas in the past several decades have not preceded a pandemic. La Nina is likely to be just one of several factors that affect a virus' spread within and between animal and human populations.
Still, anything that could help predict a pandemic would be welcomed by public health officials.
"This reinforces the need for us to be doing ongoing surveillance in human populations as well as in animal populations, and the need to look at the key elements that tie those patterns together," said Dr. Peter Rabinowitz, an environmental medicine expert at the Yale University School of Medicine, who was not involved in the study.
"The way that influenza circulates between poultry, swine, wildlife and people provides plenty of contact points that need to be better understood in order to keep us from being totally surprised," Rabinowitz said. "This holds potential, but we're still a long way off."
Peter Daszak, president of EcoHealth Alliance, a New York-based organization of scientists dedicated to the dual goals of conservation and public health, agreed with the need to improve surveillance -- both to predict pandemics and to collect the data necessary to confirm what factors are truly predictive. He called the study's results a "wake up call."
"If we start doing this properly, we might be able to beat these outbreaks before they happen," said Daszak. "It all comes down to economics. Are we prepared to do this long-term monitoring of wildlife and livestock for human pathogens? It costs money, but think about the impact of the flu: tens of billions of dollars and lives lost."