Changing weather patterns 'could trigger flu pandemics' by altering flight path of migratory birds
Swine flu pandemic of 2009: Killed 20,000 people worldwide
A weather pattern cycle that leads to a drop in the sea surface temperature across the tropical Pacific Ocean, could be responsible for spreading deadly influenza.
Scientists found that these La Nina events – when the sea temperature cools three to five celsius lower than normal – preceded the last four worldwide flu pandemics in 1918, 1957, 1968 and 2009.
The team, from Columbia University and Harvard School of Public Health, said the La Nina pattern is known
to alter the migratory patterns of birds, which are thought to be a
primary reservoir of human influenza.
They theorised that
altered migration patterns promote the development of dangerous new
strains of influenza.
flu pandemics have varied greatly in intensity – thanks in part to
modern drugs and isolation policies.
While the 'Spanish influenza' of
1918 caused an estimated 50 to 100million deaths, the latest swine flu
pandemic of 2009 claimed around 20,000 lives.
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.
that all four pandemics were preceded by a cool water anomaly off the
east coast of Papua New Guinea – consistent with the La Nina phase of
the El Nino-Southern
However, they cautioned that many La Nina events – that occur cyclically every two to seven years – have not seen novel flu strains spread across the world.
The cooler waters of La Nina – as seen as the long blue patch east of Indonesia – remained throughout 2007 and early 2008. There was a flu pandemic in 2009
A health worker gives vaccinations to chickens at a house in Egypt: La Nina may help spread bird flu by altering migratory patterns
The authors cite other research showing
that the La Nina pattern alters the migration, stopover time, fitness
and interspecies mixing of migratory birds.
These conditions could favour
the kind of gene swapping – or genetic reassortment – that creates novel
and therefore potentially more variations of the influenza virus.
Co-author Dr Jeffrey Shaman from Columbia University, said: 'We know that pandemics arise from
dramatic changes in the influenza genome.
'Our hypothesis is that La Nina
sets the stage for these changes by reshuffling the mixing patterns of
migratory birds, which are a major reservoir for influenza.'
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.
The study findings are currently published online in Proceedings of the National Academy of Sciences (PNAS).