October 29, 2008- Wild migratory birds may be more important carriers of avian influenza
viruses from continent to continent than previously thought, according
to new scientific research that has important implications for highly
pathogenic avian influenza virus surveillance in North America.
As part of a multi-pronged research effort to understand the role of
migratory birds in the transfer of avian influenza viruses between Asia
and North America, scientists with the U.S. Geological Survey (USGS),
in collaboration with the U.S. Fish and Wildlife Service in Alaska and
the University of Tokyo, have found genetic evidence for the movement
of Asian forms of avian influenza to Alaska by northern pintail ducks.
In an article published this week in Molecular Ecology,
USGS scientists observed that nearly half of the low pathogenic avian
influenza viruses found in wild northern pintail ducks in Alaska
contained at least one (of eight) gene segments that were more closely
related to Asian than to North American strains of avian influenza.
It was a highly pathogenic form of the H5N1 avian influenza virus
that spread across Asia to Europe and Africa over the past decade,
causing the deaths of 245 people and raising concerns of a possible
human pandemic. The role of migratory birds in moving the highly
pathogenic virus to other geographic areas has been a subject of debate
among scientists. Disagreement has focused on how likely it is for
H5N1 to disperse among continents via wild birds.
"Although some previous research has led to speculation that
intercontinental transfer of avian influenza viruses from Asia to North
America via wild birds is rare, this study challenges that," said Chris
Franson, a research wildlife biologist with the USGS National Wildlife
Health Center and co-author of the study. Franson added that most of
the previous studies examined bird species that are not
transcontinental migrants or were from mid-latitude locales in North
America, regions far removed from sources of Asian strains of avian
Scientists with the USGS, in collaboration with the U.S. Fish and
Wildlife Service, state agencies, and Alaska native communities,
obtained samples from more than 1,400 northern pintails from locations
throughout Alaska. Samples containing viruses were then analyzed and
compared to virus samples taken from other birds in North America and
Eastern Asia where northern pintails are known to winter. Researchers
chose northern pintails as the focus of the study because they are
fairly common in North America and Asia, they are frequently infected
by low pathogenic avian influenza, and they are known to migrate
between North America and Asia. None of the samples were found to
contain completely Asian-origin viruses and none were highly pathogenic.
"This kind of genetic analysis – using the low pathogenic strains of
avian influenza virus commonly found in wild birds – can answer
questions not only about the migratory movements of wild birds, but the
degree of virus exchange that takes place between continents, provided
the right species and geographic locations are sampled," said John
Pearce, a research wildlife biologist with the USGS Alaska Science
Center and co-author of the study. "Furthermore, this research
validates our current surveillance sampling process for highly
pathogenic avian influenza in Alaska and demonstrates that genetic
analysis can be used as an effective tool to further refine
surveillance plans across North America, Pearce added.
Website for USGS northern pintail avian influenza research:
Implications of the Research:
- Migratory bird species, including many waterfowl and shorebirds,
that frequently carry low pathogenic avian influenza and migrate
between continents may carry Asian strains of the virus along their
migratory pathways to North America.
- USGS researchers found that nearly half of influenza viruses
isolated from northern pintail ducks in Alaska contained at least one
of eight virus genes that were more closely related to Asian than North
American strains. None of the samples contained completely
Asian-origin viruses and none were highly pathogenic forms that have
caused deaths of domestic poultry and humans.
- The central location of Alaska in relation to Asian and North
American migratory flyways may explain the higher frequency of Asian
lineages observed in this study in comparison to more southerly
locations in North America. Thus, continued surveillance for highly
pathogenic viruses via sampling of wild birds in Alaska is warranted.
Future surveillance for avian influenza in wild birds should include
the type of genetic analyses used in this study to better understand
patterns of migratory connectivity between Asia and North America and
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