#17,073
A decade ago, there was still a bitter debate over whether migratory birds were A) capable of spreading HPAI viruses over long distances and B) whether migratory birds could bring Eurasian avian flu viruses to North America by crossing the Bering straits.
While it was known that some waterfowl species could carry HPAI viruses asymptomatically, the rallying cry that `Sick birds don’t fly’ was often used to argue that migratory birds couldn't be to blame for the international spread of the virus (see India: The H5N1 & Migratory Birds Debate).
In January of 2014, in response to the South Korean assertion that migratory Birds were the likely source of their H5N8 outbreak, the UN's Scientific Task Force on Avian Influenza and Wild Birds quickly issued a statement saying:
"There is currently no evidence that wild birds are the source of this virus and they should be considered victims not vectors.
A year later they would modify their stance somewhat, by saying that typically the `. . . spread of HPAI virus is via contaminated poultry, poultry products and inanimate objects although wild birds may also play a role'.
The great leap of HPAI H5N8 from Asia to North America in late 2014 (see APHIS Statement On HPAI H5 Detection Along The Pacific Flyway), and its spread to Europe, the Middle East, and Africa in 2016-17, have pretty much cemented the role of migratory birds in spreading HPAI viruses across long distances (see Migratory Birds & The Spread Of Highly Pathogenic Avian Flu).
While incursion of avian flu from Asia to Alaska (via the Pacific Flyway) had been proven in 2014, the spread from Europe across a much wider Atlantic Ocean was still thought less likely.
Still, a number of researchers thought it was possible (see 2014's PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses) with Iceland or Greenland cited as possible staging areas for bird flu.
In 2017, in Iceland Warns On Bird Flu, we saw reports suggesting that European birds carrying avian flu may have reached Iceland. Iceland is the first major landing spot for wing-weary travelers, followed by Greenland (see 2016's Avian Flu Surveillance In Greenland).
In late 2021, the inevitable happened, as HPAI H5 appears to have arrived in Eastern Canada and Western Canada via two different routes; across the Pacific and the Atlantic (Multiple Introductions of H5 HPAI Viruses into Canada Via both East Asia-Australasia/Pacific & Atlantic Flyways).
Changes in the virus - specifically the HPAI H5 clade 2.3.4.4b virus - have undoubtedly increased its ability to be spread by migratory birds, but the rapid spread of older H5N1 clades across Europe and into the Middle East and Africa over 2004-2007 also suggest long-distance carriage.
Today we've a report on two recent incursions of avian flu from Europe into Iceland, and their role in spreading the virus westward into North America. I've only posted some highlights, so follow the link to read it in its entirety.
I'll have a brief postscript after the break.
Synopsis
Iceland as Stepping Stone for Spread of Highly Pathogenic Avian Influenza Virus between Europe and North America
Anne Günther1, Oliver Krone1, Vilhjalmur Svansson1, Anne Pohlmann, Jacqueline King, Gunnar Thor Hallgrimsson, Kristinn Haukur Skarphéðinsson, Heiða Sigurðardóttir, Stefán Ragnar Jónsson, Martin Beer, Brigitte Brugger, and Timm HarderAbstract
Highly pathogenic avian influenza viruses (HPAIVs) of hemagglutinin type H5 and clade 2.3.4.4b have widely spread within the northern hemisphere since 2020 and threaten wild bird populations, as well as poultry production. We present phylogeographic evidence that Iceland has been used as a stepping stone for HPAIV translocation from northern Europe to North America by infected but mobile wild birds.
At least 2 independent incursions of HPAIV H5N1 clade 2.3.4.4b assigned to 2 hemagglutinin clusters, B1 and B2, are documented for summer‒autumn 2021 and spring 2022. Spread of HPAIV H5N1 to and among colony-breeding pelagic avian species in Iceland is ongoing. Potentially devastating effects (i.e., local losses >25%) on these species caused by extended HPAIV circulation in space and time are being observed at several affected breeding sites throughout the North Atlantic.
(SNIP)
Epidemiologic, Conservational, and Public Health Concerns of Expanded HPAIV Circulation
Our data provide evidence for 2 translocation events of HPAIV H5N1 clade 2.3.4.4b viruses from central Europe through the British Isles into Iceland observed during October 2021 with a most recent ancestor in summer 2021 (most recent common ancestor 2021.5). Onward transmission to Newfoundland and possibly additional regions in the North Atlantic raises several concerns.
(SNIP)
Increased alertness should now also extend to the Southern Hemisphere. In the 2 reported incursion events of gs/GD HPAI viruses into North America by migrating wild birds, during 2014 and 2021/2022, virus spread along the Pacific (2014) and the Atlantic coast line (2021) from north to south and further inland affecting wild birds and poultry in Canada, as well as in most of the United States (7–9). However, for unknown reasons, spread seems to be interrupted between North America and South America because no incursions had been reported during 2014/2015 or since 2021 from the Caribbean region and South America.
Similar observations have been made along the east side of the Pacific Ocean. Despite endemic presence of gs/GD HPAIV in several regions of Southeast Asia, and frequent incursions into migratory wild bird populations, cases have so far not been reported from Australia/Oceania (4). It is only at the most southern tip of Africa that gs/GD-like HPAIVs have reached and stayed within the Southern Hemisphere. However, this bridgehead of the virus might put geographically sequestrated subantarctic species, such as penguins and albatrosses, or the highly endangered avifauna of New Zealand at increased risk for exposure.
In conclusion, as shown by the rapid and devastating spread of HPAIV H5N1 through poultry holdings in North America after primary incursions from infected wild birds (10), the avian‒human interface has expanded again. Infections in 1 human (25) and in several terrestrial scavenging carnivores, such as foxes, skunks, and raccoons (12), illustrate the increased risk for spillover transmissions.
Dr. Guenther is a veterinarian and a doctoral candidate at the Friedrich-Loeffler-Institute, Greifswald–Insel Riems, Germany. Her primary research interests are avian viruses and other pathogens with potential influence on avian species conservation and public health.
