Jeffrey Shemen of Columbia University (USA) and his colleagues concluded that La Niña can cause an influenza pandemic.
The scientists found that the last four pandemics follow La Niney — natural phenomenon, characterized by cooling the surface of the eastern Pacific Ocean. On the other hand, not every La Niña led to a pandemic, so to their own conclusions, the authors are careful. Most likely, some climate events is not enough here to work a few more factors.
The last four pandemics — a "Spanish flu" in 1918, the Asian flu of 1957, Hong Kong 1958-th and "swine" of 2009.
The reason for the correlation remains a mystery. Pandemic strains occur when the two types of influenza virus are found in the animal (birds or pigs) and exchange genetic material. The output is a strain to which humans are not immune. It is also noticed that the La Niña as a phenomenon has a tremendous influence on the weather of the entire planet, changing the routes of migratory birds and the molt. As a result, in the same places on holiday can stay for bird species that in other years (when there is no La Nini) do not occur, and viruses are more choices.
In anticipation of a pandemic "swine flu" wild birds — native precursor pandemic strain could visit farms and infect poultry, and that the virus is transmitted pig, in which the body and formed the final version of the strain. A similar series of matches could well be the case.