Global dissemination of Influenza A virus is driven by wild bird migration through arctic and subarctic zones

Influenza A viruses (IAV) circulate endemically among many wild aquatic
bird populations that seasonally migrate between wintering grounds in
southern latitudes to breeding ranges along the perimeter of the
circumpolar arctic. Arctic and subarctic zones are hypothesized to serve
as ecologic drivers of the intercontinental movement and reassortment of
IAVs due to high densities of disparate populations of long distance
migratory and native bird species present during breeding seasons. Iceland
is a staging ground that connects the East Atlantic and North
Atlantic American flyways, providing a unique study system for
characterizing viral flow between eastern and western hemispheres. Using
Bayesian phylodynamic analyses, we sought to evaluate the viral
connectivity of Iceland to proximal regions and how inter-species
transmission and reassortment dynamics in this region influence the
geographic spread of low and highly pathogenic IAVs. Findings demonstrate
that IAV movement in the arctic and subarctic follows seabird migration
around the perimeter of the circumpolar north, favoring short-distance
flights between proximal regions rather than long distance flights over
the polar interior. Iceland connects virus movement between mainland
Europe and North America, particularly due to the westward migration of
wild birds from mainland Europe to Northeastern Canada and Greenland.
Though virus diffusion rates were similar among avian taxonomic groups in
Iceland, gulls act as recipients and not sources of IAVs to other avian
hosts prior to onward migration. These data identify patterns of virus
movement in northern latitudes and inform future surveillance strategies
related to seasonal and emergent IAVs with pandemic potential.