East and Southeast Asian regions are the cradles of seasonal flu viruses

April 17th, 2008 - 1:47 pm ICT by admin  

Washington, April 17 (ANI): New research depicts East and Southeast Asian regions to be the cradles of the viruses that lead to seasonal flu, say scientists at the University of Cambridge.

The researchers, who carried out the study in collaboration with experts from the World Health Organisation (WHO) Global Influenza Surveillance Network, found that viruses that originate in East and Southeast Asia and migrate around the world give rise to the most common type of influenza virus called A (H3N2).

The study revealed that since 2002, influenza A (H3N2) viruses have migrated out of the East and Southeast Asian circulation network, which includes tropical, subtropical and temperate countries, and spread throughout the world.

Colin Russell and his colleagues at the University of Cambridge analysed 13,000 samples of influenza A (H3N2) virus, collected worldwide by the World Health Organization Global Influenza Surveillance Network between 2002 and 2007.

The analyses provided them with fresh insights into different strains of A (H3N2), the subtype of seasonal flu that causes the most disease, as they arrived at new locations around the world over the five-year period.

Describing their findings in the journal Science, the researchers revealed that the new strains emerge in East and Southeast Asia, and then about six to nine months later reach Europe and North America.

The strains take several more months to reach South America, they add.

According to the group, the studys results also show that the viruses rarely return to East and Southeast Asia after leaving the region, suggesting that places outside these regions are the evolutionary graveyards of influenza viruses.

In their study report, the researcher also write that flu epidemics typically occur during the winter months in the temperate regions of the northern and southern hemisphere and in tropical countries, flu epidemics often coincide with the rainy season.

They say that since there is variation in the timing of the rainy season in different parts of East and Southeast Asia, combined with the wintertime epidemics in the temperate parts of the region, the overlap in the timing of epidemics gives the opportunity for influenza viruses to circulate year round in East and Southeast Asia.

Flu epidemics appear to be driven by seasonal factors such as winter, or rainy seasons. So there can be cities that are only 700 miles away from each other, such as Bangkok and Kuala Lumpur, which have epidemics six months apart. There is a lot of variability like this in East and Southeast Asia, so lots of opportunity for an epidemic in one country to seed an epidemic to another nearby country, like a baton passed by runners in a relay race, said Derek Smith of the University of Cambridge, who is the corresponding author of the study.

The discovery attains significance as it may make the way for further improvement in flu vaccines, and make the evolution of the virus more predictable.

The ultimate goal of our collaboration is to increase our ability to predict the evolution of influenza viruses. This study is one step along that path and in particular highlights the importance of ongoing collaborations and surveillance in East and Southeast Asia, and expanding these collaborations in the future, said Smith. (ANI)

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