Flu Viruses’ Global Pathways Largely Predictable

We’ll be addressing globalizing issues in intro to IR on Monday and this interesting story in the Washington Post from a couple of days ago illustrates some of the important concepts raised in Chapter 10 of Mingst.

New strains of seasonal influenza virus all arise in East or Southeast Asia and take a largely predictable route around the world before dying out for good in South America, the global glue-trap for the pathogen.

That is the conclusion reported yesterday by a large team of researchers who analyzed the genetic ancestry of about 13,000 virus samples collected from six continents over a five-year period to answer long-standing questions about the flu’s life cycle.

The findings help explain the biological mechanisms that underlie two long-held observations about flu: New strains tend to appear first somewhere near China, and Australia’s flu season is a preview of what will happen in North America six months later. They also help explain why one winter’s flu is always at least a little bit different from the previous winter’s, even though the virus disappears over the summer…

…But why is East-Southeast Asia always the starting point? The researchers believe it’s because of the unusual concentration of different climates there. The region has both tropical environments, where flu flourishes during the rainy season, and temperate zones. There are places that are relatively close — Russell cited Bangkok and Kuala Lumpur, Malaysia, 700 miles apart — that have totally different flu seasons.

This effectively allows new strains to be passed around the region like a baton in a relay race, even though in each climate zone the virus completely dies out once a year.

The reason new variants don’t cause epidemics if they are carried back to East Asia from elsewhere is because people already have immunity to them. They’re old news. At least that’s the theory.

Here, from Science magaizine (subscription only) is a chart demonstrating the global spread of flu viruses.