The densely packed cities of East and Southeast Asia act as incubators for new strains of deadly influenza viruses that get exported around the globe, new research shows.
Two new studies show that the virus spreads in waves through cities such as Hong Kong and Bangkok before hitching rides upon human hosts to other regions.
"For over 60 years, the global migration of influenza viruses has been a mystery," said study author Colin Russell of the University of Cambridge in the United Kingdom.
Now the new findings will help scientists better predict the evolution of the most common type of influenza virus, A (H3N2), which could in turn lead to improved flu vaccines, the authors said.
(See photos of people fighting the spread of influenza.)
Evolutionary Graveyards
Russell and colleagues analyzed 13,000 samples of influenza A (H3N2) virus gathered across six continents from 2002 to 2007. Their findings appear in this week's issue of the journal Science.
The team used a new technique called antigenic cartography to make fine-grained measurements of genetic differences between strains.
They focused on the gene that encodes for hemagglutinin, a protein on the virus's protective shell that plays an important role in infection.
The team's analysis allowed them to identify different viral strains as they traveled around the world.
New strains first appeared in East and Southeast Asia and reached Europe and North America about six to nine months later.
Several months after that the viruses arrived in South America.
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