# 5963
Southeast Asia has long been considered `the cradle of influenza’, an area of the world where influenza viruses circulate year round, more than a billion people live in close proximity, and where humans and farm animals often come into close contact with one another.
An ideal breeding ground, and launching pad, for flu pandemics.
During the 20th century, 2 of the 3 influenza pandemics (1957 Asian Flu, 1968 Hong Kong Flu) originated from this region.
But new research on the the spread of influenza A, published yesterday in PNAS, indicates that Southeast Asia isn’t the only birthplace of the flu.
The dauntingly titled open access study can be found at:
Temporally structured metapopulation dynamics and persistence of influenza A H3N2 virus in humans
Published online before print November 14, 2011, doi: 10.1073/pnas.1109314108 PNAS November 14, 2011
Justin Bahl, Martha I. Nelson, Kwok H. Chan, Rubing Chen, Dhanasekaran Vijaykrishna, Rebecca A. Halpin, Timothy B. Stockwell, Xudong Lin, David E. Wentworth, Elodie Ghedin, Yi Guan, J. S. Malik Peiris, Steven Riley, Andrew Rambaut, Edward C. Holmes, and Gavin J. D. Smith
(EXCERPT)
Although the virus population that migrated between Southeast Asia and Hong Kong persisted through time, this was dependent on virus input from temperate regions and these tropical regions did not maintain a source for annual H3N2 influenza epidemics.
We further show that multiple lineages may seed annual influenza epidemics, and that each region may function as a potential source population. We therefore propose that the global persistence of H3N2 influenza A virus is the result of a migrating metapopulation in which multiple different localities may seed seasonal epidemics in temperate regions in a given year.
Such complex global migration dynamics may confound control efforts and contribute to the emergence and spread of antigenic variants and drug-resistant viruses.
The entire study is available online, but for those of us who find the finer details of Bayesian phylogeographic analysis of viral migration above our pay grade, we’ve a press release from Duke University Medical Center that helps summarize this paper.
Study finds tropical areas aren't the only source of seasonal flu
DURHAM, N.C. and SINGAPORE – A commonly held theory says that flu virus originates every year in Southeast and Eastern Asia, making this region the source of seasonal flu epidemics in other parts of the world.
However, researchers at Duke-NUS Graduate Medical School in Singapore have found that influenza virus in tropical areas isn't the only global source of flu epidemics. The international team of scientists involved in the work found that any one of the urban centers they studied could act as a source for a flu epidemic in any other locality.
"We found that these regions are just one node in a network of urban centers connected by air travel, through which flu virus circulates and causes a series of local epidemics that overlap in time," said Gavin Smith, PhD, senior author and Associate Professor in the Program in Emerging Infectious Diseases at Duke-NUS.
The study was published the week of Nov. 14 in the online Early Edition of the Proceedings of the National Academy of Sciences.
The research team chose to study influenza A because it is much more prevalent than both influenza B and C. Influenza is a significant cause of human illness and death worldwide – the World Health Organization estimates that 250,000 to 500,000 influenza A related deaths occur per year worldwide, and about 49,000 deaths occur in the United States.
The team obtained RNA sequences of virus samples from 2003 to 2006 in Australia, Europe, Japan, New York, New Zealand and Southeast Asia, as well as some more recently sequenced viruses from Hong Kong. The virus populations from tropical Southeast Asia and Hong Kong showed relatively low levels of genetic diversity and no seasonal fluctuations in comparison with annual temperate-area epidemics.
The analysis used time and space parameters to reveal high rates of viral migration among the urban centers tested. Although the virus population that migrated between Southeast Asia and Hong Kong persisted through time, the pattern of infections also depended on virus input from temperate regions that have distinct seasons. None of the temperate and tropical regions they examined was the source of all of the new flu strains in a given year.
The scientists showed that multiple lineages of a virus could seed annual flu epidemics, and that each region could function as a potential source population.
Six weeks before the 2009 H1N1 pandemic virus emerged in Mexico, I wrote blog called:
Sunday, March 08, 2009
How The Next Pandemic Will Arrive
# 2876
There is a lot we don't currently know about the next pandemic. We don't know when it will arrive. We don't know what virus will cause it. And we don't know how bad it will be.
But there is one thing almost certain.
It will arrive in most countries by airplane.
The video above, which as been making the rounds for several months, was made by ZHAW (Zürcher Hochschule für Angewandte Wissenschaften) or The Zurich University of Applied Sciences.
Before the advent and explosion in international air travel, the tropical regions of Southeast Asia probably played a much bigger role in the the creation, incubation, and spread of influenza viruses.
With man’s help, influenza today has become an accomplished world traveler. No longer are we protected by vast oceans and long transit times.
New strains and viral reassortments that a few decades ago might have sputtered and died out unnoticed in some remote region of the world, or have been detected and quarantined aboard slow moving ships, can now hop a plane and find new hosts in a matter of hours.
Something we saw as recently as the 2009 H1N1 pandemic, which began not in Asia, but in the Americas.
Further proof that as the world evolves and become more complex, so does the threat from emerging infectious diseases.
