Although the arrival of HPAI H5 viruses of Eurasian origin to North America this winter was met with surprise, it wasn’t a completely unexpected event. For years we’ve watched as the USGS and the U.S. Fish and Wildlife Service in Alaska have worked to test and track bird migrations and the avian influenza viruses they carry.
In 2008, in USGS: Genetic Evidence Of The Movement Of Avian Influenza Viruses From Asia To North America, we saw evidence that suggested migratory birds play a larger role in intercontinental spread of avian influenza viruses than previously thought.
A couple of years later, in Where The Wild Duck Goes, we looked at a USGS program that used Satellite Tracking To Reveal How Wild Birds May Spread Avian Flu. While it was H5N8 that finally made the jump to north America, at the time, the HPAI fear was from the H5N1 virus . From the report:
“Because northern pintails in Alaska exchange influenza viruses with Asian birds, movement of the H5N1 virus into eastern Russia would increase the risk for its transmission to North America via wild birds -- such as the northern pintail -- that migrate between continents,” said Hupp.
Although Atlantic crossing migratory birds are considered potential vectors of avian flu (see The North Atlantic Flyway Revisited), the relatively short distance between Alaska and Siberia – a preferred summer nesting spot for many migratory species – makes the Pacific flyway particularly vulnerable.
Yesterday a new study was published in the Journal Virology which provides even more evidence of this intercontinental avian influenza exchange program.
Andrew M. Rameya, , , Andrew B. Reevesa, Sarah A. Sonsthagena, Joshua L. TeSlaab, Sean Nasholdb, Tyrone Donnellya, Bruce Caslerc, Jeffrey S. Hallb
- • 2924 wild bird samples from western Alaska were screened for influenza A viruses.
- • Among 90 viral isolates recovered were two viruses of the H9N2 subtype.
- • H9N2 subtype isolates were nearly identical with viruses from China and South Korea.
- • Results provide evidence for intercontinental viral dispersal by migratory birds.
Samples were collected from wild birds in western Alaska to assess dispersal of influenza A viruses between East Asia and North America. Two isolates shared nearly identical nucleotide identity at eight genomic segments with H9N2 viruses isolated from China and South Korea providing evidence for intercontinental dispersal by migratory birds.
Additional background information is provided by the following USGS press release.
Released: 3/31/2015 1:00:00 PM
ANCHORAGE, Alaska — In a new study published today, scientists from the U.S. Geological Survey and U.S. Fish and Wildlife Service harnessed a new type of DNA technology to investigate avian influenza viruses in Alaska. Using a “next generation” sequencing approach, which identifies gene sequences of interest more rapidly and more completely than by traditional techniques, scientists identified low pathogenic avian influenza viruses in Alaska that are nearly identical to viruses found in China and South Korea.
The viruses were found in an area of western Alaska that is known to be a hot spot for both American and Eurasian forms of avian influenza.
“Our past research in western Alaska has shown that 70 percent of avian influenza viruses isolated in this area were found to contain genetic material from Eurasia, providing evidence for high levels of intercontinental viral exchange,” said Andy Ramey, a scientist with the USGS Alaska Science Center and lead author of the study. “This is because Asian and North American migratory flyways overlap in western Alaska.”
The new study, led by the USGS, found low pathogenic H9N2 viruses in an Emperor Goose and a Northern Pintail. Both of the H9N2 viruses were nearly identical genetically to viruses found in wild bird samples from Lake Dongting, China and Cheon-su Bay, South Korea.
“These H9N2 viruses are low pathogenic and not known to infect humans, but similar viruses have been implicated in disease outbreaks in domestic poultry in Asia,” said Ramey.
There is no commercial poultry production in western Alaska and highly similar H9N2 virus strains have not been reported in poultry in East Asia or North America, so it is unlikely that agricultural imports influenced this result.
The finding provides evidence for intercontinental movement of intact avian influenza viruses by migratory birds. The USGS recently released a publication about the detection of a novel highly pathogenic H5N8 virus in the U.S. that is highly similar to the Eurasian H5N8 viruses. This suggests that the novel re-assortment may be adapted to certain waterfowl species, enabling it to survive long migrations. That virus, and associated strains, have now spread from early detections in wild and domestic birds in Pacific states to poultry outbreaks in Minnesota, Missouri and Arkansas.
“The frequency of inter-hemispheric dispersal events of avian influenza viruses by migratory birds may be higher than previously recognized,” said Ramey.
While some of the samples for the project came from bird fecal samples collected from beaches at Izembek National Wildlife Refuge, most of the samples came from sport hunters.
“For the past several years, we’ve worked closely with sport hunters in the fall to obtain swab samples from birds and that has really informed our understanding of wildlife disease in this area,” said Bruce Casler, formerly a biologist with the USFWS Izembek National Wildlife Refuge and a co-author of the study. None of the viruses found in harvested birds from Izembek Refuge are known to infect humans, but hunters should always follow safe meat handling and cooking guidelines when processing wild game.
The paper, “Dispersal of H9N2 influenza A viruses between East Asia and North America by wild birds” was published today in the journal Virology. A summary of all samples collected at the Izembek Refuge will be described in a subsequent publication.
Additional information about avian influenza can be found at the following web sites:
For years the rallying cry that `Sick birds don’t fly’ has been used to argue that migratory birds aren’t to blame for the spread of the virus, even though it has been shown that some species of birds (particularly ducks) can carry – and presumably spread – the virus asymptomatically.
A recent statement by the UN CMS/FAO Co-Convened Scientific Task Force on Avian Influenza and Wild Birds maintains that typically the spread of HPAI virus is via contaminated poultry, poultry products and inanimate objects although wild birds may also play a role.
We explored the often bitter debate between the poultry industry and conservationists over the role of migratory birds in spreading avian flu in Bird Flu Spread: The Flyway Or The Highway?, and while poultry industry practices often factor heavily, it is hard to refute the notion that wild birds are at least partially responsible.
For more on the role of migratory birds, you may wish to revisit: