Children in Turkey Die From H5 Flu, But How Did It Get There?

CNN is reporting that infection with an avian flu strain has resulted in the death of a 3rd child in Turkey.  The three siblings evidently contracted the virus from sick poultry, domesticated chickens that had been killed and cooked after falling ill.  The WHO is still waiting for confirmation on whether the strain is H5N1.

The simple explanation for the appearance in Turkey of H5N1 is transmission by migratory birds.  However, a recent AP story by Andrew Bridges suggests that, "Avian Flu [is] Not Spread by Bird Migration" (at LiveScience):

Bird flu appears more likely to wing its away around the globe by plane than by migrating birds. Scientists have been unable to link the spread of the virus to migratory patterns, suggesting that the thousands of wild birds that have died, primarily waterfowl and shore birds, are not primary transmitters of bird flu.

If that holds true, it would suggest that shipments of domestic chickens, ducks and other poultry represents a far greater threat than does the movement of wild birds on the wing.

...Reports this summer and fall of the spread of the H5N1 strain strongly suggested wild birds were carrying the disease outward from Asia as they followed migration patterns that crisscross the Earth. The timing and location of outbreaks in western China, Russia, Romania, Turkey and Croatia seemed to point to wild birds en route to winter grounds.

Since the early fall, however, there have been only scattered reports of more outbreaks. The disease has been glaringly absent, for example, from western Europe and the Nile delta, where many presumed it would crop up as migrating birds returned to winter roosts.

...That has made increasing the understanding of the migratory routes followed by birds more important than ever. It also draws attention to how little is still known about the routes.

This last point is the most important observation of the whole article.  We simply don't know enough about the virus or its wild reservoir, and we definitely aren't spending enough to remedy our ignorance.

But assume for a moment the virus now killing people in Turkey is H5N1, then here's the thing: if the virus is spread more by human travel or by shipments of birds, as Mr. Bridges' article suggests, how the hell did it wind up in a relatively remote village in Turkey?  Is there sufficient poultry trade or human travel between southeastern Anatolia and SE Asia to serve as a conduit for an avian influenza virus?  This trade and travel must be only a small fraction of that between SE Asia and North America, Europe, and Japan.

This means that either the virus "got lucky" this time, based on whatever trade and travel does exist between SE Asia and Anatolia, or that the virus is much easier to spread than we now believe.  But if it is really spread mostly by human action, then it should be all over the globe by now, or it soon will be.  Which leads me to suspect that migratory birds are in fact the vector, and that we need to do a much better job of understanding the virus in the wild.

A potential reason why the virus has not spread as much as feared this year can be found in an article by Howard Markel in the last Week in Review section of The New York Times.  In a short piece entitled, "If the Avian Flu Hasn’t Hit, Here’s Why. Maybe.", Dr. Markel, a professor of pediatrics and communicable diseases at the University of Michigan, suggests that, "Wild birds have completed their seasonal migration, and it appears that the United States has dodged the avian flu threat for now. The pattern of the semiannual migration itself provides some protection."

The article is accompanied by a graphic illustrating the mostly north-south orientation of migratory pathways.  Dr. Markel's hypothesis is that because there is very little east-west overlap of flyways, there is only a small chance every year for the virus to be transmitted to birds in adjacent flyways.

I think we don't have the geographical/migration data to be so confident about the boundaries of flyways.  All those charts have a very "drawn by hand" feel to them.   Moreover, this is just one component of our ignorance.  Thus while Dr. Markel may well be correct, it is quite difficult to presently sort out the effects of species tropism from geographical distribution and spread.  Then there is all of our ignorance about the basic molecular biology of the virus, and whether this is the big one or not, about which I have written many posts.

Dr. Markel concludes, "It is possible that avian flu may never pose an epidemic threat to humans. But for now, the best way to reduce the danger is to keep watching the birds."