This question was discussed yesterday in the comments to this post. An article in yesterday's New Scientist offers some ideas:
But New Scientist can reveal that the location of Africa's first reported outbreak should not come as a surprise. The region affected is right beside a major wintering ground for two relatively common species of duck. Those ducks shared breeding grounds in Siberia last summer with birds that winter in Turkey and around the Black Sea, where the virus also appeared recently.
Furthermore, Kano is near the Hadejia-Nguru inland river delta, which is a major wintering location for Northern pintail and garganey ducks. These species summer in breeding grounds across Siberia, where the Qinghai strain of H5N1 infected poultry and wild birds in summer 2005. They then winter in Turkey, around the Black Sea, and in West Africa. The Qinghai strain has already broken out in Turkey and around the Black Sea, apparently carried by migrants.
The authoritative 1996 Atlas of Anatidae [ducks, geese and swans] Populations of Africa and Western Europe says the Northern pintail wintering in the Black Sea and Mediterranean basins "are lumped with those wintering in West Africa as a single large population". On average, 18,000 pintails winter each year at Hadejia-Nguru. Similar numbers of garganey ducks follow the same migration and 500,000 of each species winter at nearby Lake Chad.
Some of the Northern pintail wintering now in Britain and along Europe's North Sea and Atlantic coasts also spent last summer on the same breeding grounds as the pintail that subsequently flew to the Black Sea, Turkey and West Africa.
So, there's one explanation. I'm not enough of a bird person to know if it's a good one or not, however.
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Interesting.
Now if all this is indeed relevant to the spread of H5N1 in water-fowl, then the fact that the East Atlantic Flyway intersects the East Africa/West Asia Flyway in Nigeria is cause for great concern, as that seems to provide a potential route for spread to all of western Africa and to North America via Labrador, Northern Quebec or the Canadian High Arctic.
Edited to add:
As grrlscientist correctly notes, we should not get TOO carried away with our extrapolations (and by 'we' I mean 'me'). There's still nothing solid to nail wild birds via natural migrations as a significant means of spreading this virus around, as compared to other routes.
She notes -
Yet, despite the fact that wild birds are now carrying H5N1 across long distances during migration, the data still do not show that wild birds are a significant source of the virus in local areas, nor do they spread the virus to humans. Instead, domestic poultry serve as the primary source ...
BirdLife International has some interesting articles examining the extent to which migratory birds might be spreading H5N1 The BirdLife articles echo the point Dave & grlscientist make above. From the Birdlife Avian Influenza FAQ:
"If wild birds have any role, it is minor compared to other mechanisms...All the evidence suggests that H5N1 is highly lethal to migratory wild bird species, and kills them quickly; that infected migrants cannot move long distances; and that the virus is most likely to be contracted locally, close to the site of deaths."
BirdLife goes on to identify the (suspected) main sources of H5N1 spread in: Are high risk farming practices spreading avian flu? In that article they note:
"When plotted, the pattern of outbreaks follows major road and rail routes, not flyways...Movement of infected poultry and poultry products is a likely cause of spread."
Great possible connection for the spread of avian flu. It is very realistic to me, but then I'm a fan of the thought that sheep scrapie disease has caused the chronic wasting disease epidemic in wild deer populations in Colorado. Amazing to me the way everything has links that we do not realize, and how much information can be accumulated/disseminated with others on the net. Will be interesting to see what further links in this infectious chain may show up.
That scenario sounds quite plausible, but it's dull.
Try this one:
Voodoo priests at risk of bird flu
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