The spread of Influenza in 1918, 1957, 1968 and 2009 was responsible for a number of deaths and infections. A lot of research has been done on the same and similar weather patterns were reflected which showed that each of these times were preceded by La Nine conditions in the equatorial Pacific. Such kind of weather pattern basically alters the migratory patterns of birds which are responsible for human influenza. The altered migration patterns are predominantly and primarily responsible for the cause of influenza.
In order to study the relationship between the weather patterns and mass epidemics, the researchers studied the temperature of the ocean in the equatorial Pacific in the fall and winter before the outbreak of the mass flu epidemics. It was found that all of these were preceded by below-normal sea surface temperatures. Such kind of pattern generally develops in the tropical Pacific ocean in a period of two and seven years.
Other research aspects propagate that the La Nina pattern is quite responsible for bringing about a change in the migration, stopover time, fitness and interspecies mixing of migratory birds. Such conditions are quite apt for the birth of a number of variations of the influenza virus due to gene swapping or genetic reassortment. As per Jeffrey Shaman, PhD, Mailman School assistant professor of Environmental Health Sciences and co-author of the study, such pandemics are known to cause due to the changes in the influenza genome. Besides, what can be inferred is that these changes have their basis in La Nina pattern which reshuffles the mixing patterns of migratory birds that are responsible for spreading influenza.
If there are changes in the migration pattern then they can have several consequences. They can not only change the pattern of contact among bird species but also influence the way in which the birds will come into contact with the domestic animals including pigs. In fact, it has been established that the swine flu epidemic spread in 2009 which created a lot of hype across the world was a result of gene-swapping between avian and pug influenza viruses.
Thus flu pandemics and La Nina are strongly related and in fact the link between the influenza pandemics as well as strong El Nino events has also been established in the recent papers. A lot of tests are still being conducted to establish strong relationships.