Global Flyways – Credit FAO
It is pretty clear from the way the HPAI H5N1 virus spread out of South East Asia to Europe and the Middle East in the middle of the last decade, that migratory birds can play a major role in its dissemination. Many species are able to carry avian influenza viruses without ill effect, and when they encounter other birds, can `share’ their viral cargo along their migratory flyway.
Where flyways overlap, there is a greater chance of spreading a virus from one region to another. And as you can see by the map above, they overlap a lot.
During the peak of H5N1’s great expansion during the middle of the last decade, the number of countries affected by that emerging avian virus jumped from 16 to over 60 in less than 24 months (see OIE 63 Countries Report H5N1 Avian Influenza in Domestic Poultry/Wildlife 2003-2010).
And for awhile, there were concerns that the virus would eventually wing its way to North America – with the most likely route viewed as coming from Siberian birds crossing the Bering Straits into Alaska and Canada. When that didn’t happen, and when the H5N1 threat in Europe retreated, many concluded we were `protected’ from such viral intrusions by both distance and oceans.
Last March, when our infectious disease attentions were pretty much evenly divided between MERS in the Middle East and the winding down of the second wave of H7N9 in China, I blogged on a study that appeared in PLoS One that looked at the potential for European Avian flu viruses to hop the Atlantic and end up in North America (see Thursday, March 20, 2014 PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses).
In view of the recent emergence of a new, highly pathogenic avian influenza virus (H5N8) now turning up in Europe – and the fact this study probably didn’t get the attention it deserved last spring - it seems appropriate to revisit that study (funded by the USGS and NIAID) that confirms at least the potential of avian flu viruses to cross the Atlantic to reach North America.
First the press release from the USGS, then a link to the study and some excerpts. I’ll have a bit more after.
Released: 3/19/2014 5:10:00 PM
The North Atlantic region is a newly discovered important pathway for avian influenza to move between Europe and North America, according to a U.S. Geological Survey report published today.
USGS scientists and Icelandic partners found avian flu viruses from North America and Europe in migratory birds in Iceland, demonstrating that the North Atlantic is as significant as the North Pacific in being a melting pot for birds and avian flu. A great number of wild birds from Europe and North America congregate and mix in Iceland's wetlands during migration, where infected birds could transmit avian flu viruses to healthy birds from either location.
By crossing the Atlantic Ocean this way, avian flu viruses from Europe could eventually be transported to the United States. This commingling could also lead to the evolution of new influenza viruses. These findings are critical for proper surveillance and monitoring of flu viruses, including the H5N1 avian influenza that can infect humans.
"None of the avian flu viruses found in our study are considered harmful to humans," said Robert Dusek, USGS scientist and lead author of the study. "However, the results suggest that Iceland is an important location for the study of avian flu and is worthy of special attention and monitoring."
The study also highlighted the new finding that gulls play an important role in moving avian flu viruses across the North Atlantic.
During the spring and autumn of 2010 and autumn of 2011, the USGS researchers and Icelandic partners collected avian influenza viruses from gulls and waterfowl in southwest and west Iceland (see map). By studying the virus’ genomes — an organism’s hereditary information — the researchers found that some viruses came from Eurasia and some originated in North America. They also found viruses with mixed American-Eurasian lineages.
"For the first time, avian influenza viruses from both Eurasia and North America were documented at the same location and time," said Jeffrey Hall, USGS co-author and principal investigator on this study. "Viruses are continually evolving, and this mixing of viral strains sets the stage for new types of avian flu to develop."
Excerpts from PLoS One:
Robert J. Dusek mail, Gunnar T. Hallgrimsson, Hon S. Ip, Jón E. Jónsson, Srinand Sreevatsan, Sean W. Nashold, Joshua L. TeSlaa, Shinichiro Enomoto, Rebecca A. Halpin, Xudong Lin, Nadia Fedorova, Timothy B. Stockwell, Vivien G. Dugan, [ ... ], Jeffrey S. Hall
Avian influenza virus (AIV) in wild birds has been of increasing interest over the last decade due to the emergence of AIVs that cause significant disease and mortality in both poultry and humans. While research clearly demonstrates that AIVs can move across the Pacific or Atlantic Ocean, there has been no data to support the mechanism of how this occurs. In spring and autumn of 2010 and autumn of 2011 we obtained cloacal swab samples from 1078 waterfowl, gulls, and shorebirds of various species in southwest and west Iceland and tested them for AIV. From these, we isolated and fully sequenced the genomes of 29 AIVs from wild caught gulls (Charadriiformes) and waterfowl (Anseriformes) in Iceland. We detected viruses that were entirely (8 of 8 genomic segments) of American lineage, viruses that were entirely of Eurasian lineage, and viruses with mixed American-Eurasian lineage. Prior to this work only 2 AIVs had been reported from wild birds in Iceland and only the sequence from one segment was available in GenBank. This is the first report of finding AIVs of entirely American lineage and Eurasian lineage, as well as reassortant viruses, together in the same geographic location. Our study demonstrates the importance of the North Atlantic as a corridor for the movement of AIVs between Europe and North America.
Our data demonstrate that the North Atlantic serves as a route for intercontinental movement of AIV and it will be important to track the further dissemination of these viruses, in whole, or in part, into the Icelandic avian community and, more significantly, into the avian communities of Europe or North America.
For more on the geographic expansion of bird flu viruses, you may wish to revisit: