Intercontinental Spread of Asian-Origin H5N8 to North America through Beringia by Migratory Birds

Abstract

Phylogenetic network analysis and understanding of waterfowl migration patterns suggest that the Eurasian H5N8 clade 2.3.4.4 avian influenza virus emerged in late 2013 in China, spread in early 2014 to South Korea and Japan, and reached Siberia and Beringia by summer 2014 via migratory birds. Three genetically distinct subgroups emerged and subsequently spread along different flyways during fall 2014 into Europe, North America, and East Asia, respectively. All three subgroups reappeared in Japan, a wintering site for waterfowl from Eurasia and parts of North America.

FIG 1

Median-joining phylogenetic network of HPAI H5 clade 2.3.4.4 viruses. The median-joining network was constructed from the HA-encoding gene. This network includes all of the most parsimonious trees linking the sequences. Each unique sequence is represented by a circle whose size reflects the frequency of the sequence in the data set. Branch length is proportional to the number of mutations. Isolates are colored according to the origin and season of the sample as follows: red inner circle, poultry farm isolates; purple inner circle, wild-bird isolates; black outer circle, early 2014 isolates; blue outer circle, late 2014 isolates.

FIG 2

Geographic map showing the movement of H5N8 HPAIV in Asia, Europe, and North America in relation to regional waterfowl migration routes. The map, by Dmthoth, is from Wikipedia Commons (http://commons.wikimedia.org/wiki/File:Blank_Map_Pacific_World.svg).