Ducks Carry Bird Flu From Asia to Alaska

Ducks Carry Bird Flu From Asia to Alaska





October 2008 - Wild migratory birds appear to 
be important carriers of avian influenza viruses from continent to 
continent, according to new research that scientists say has important 
implications for highly pathogenic avian influenza virus surveillance in 
North America. 
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. 
Scientists with the U.S. Geological Survey, in collaboration with the U.S. 
Fish and Wildlife Service in Alaska and the University of Tokyo, have 
found genetic evidence that northern pintail ducks carried Asian forms of 
avian influenza to Alaska. 
"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. 
Most 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 influenza, Franson said. 
For this study, 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 analyzed and compared to virus samples 
taken from other birds in North America and Eastern Asia where northern 
pintails are known to winter. 

The 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 bird flu. 
None of the samples were found to contain completely Asian-origin viruses 
and none were highly pathogenic. 
The low pathogenic form of the disease commonly causes only mild symptoms 
such as ruffled feathers and a drop in egg production, and may easily go 
undetected. 
The highly pathogenic form is far more dramatic. It spreads very rapidly 
through poultry flocks, causes disease affecting multiple internal organs, 
and has a mortality that can approach 100 percent, often within 48 hours. 
Under the crowded conditions of intensive poultry farming, some variants 
of the H5 and H7 viral subtypes derived from wild birds can evolve into 
highly pathogenic avian influenza viruses. 
It was a highly pathogenic form of the H5N1 bird flu virus that spread 
across Asia to Europe and Africa over the past decade, causing the culling 
of hundreds of millions of chickens and ducks, and the deaths of 245 
people, raising concerns of a possible human pandemic. 
Avian influenza viruses do not normally infect humans but there have been 
instances of certain highly pathogenic strains causing severe respiratory 
disease in humans. In most cases, the people infected had been in close 
contact with infected poultry or with objects contaminated by their feces. 

Still, there is concern that the virus could mutate to become more easily 
transmissible between humans, raising the possibility of an influenza 
pandemic. 
In June, the Centers for Disease Control and Prevention in Atlanta 
released results of a study suggesting that some North American avian 
influenza A H7 virus strains have properties that might enhance their 
potential to infect humans and their potential to spread from human to 
human. 
"We know that influenza viruses are constantly changing and that is why 
it's so important to watch them carefully," explained Dr. Jessica Belser, 
CDC lead author on the project. "In this study, we discovered that some 
recently identified avian influenza A H7 viruses have some properties that 
could enhance their potential to infect people and possibly spread among 
people." 
The role of migratory birds in moving the highly pathogenic virus to other 
geographic areas has been a subject of disagreement among scientists that 
focused on how likely it is for H5N1 to disperse across continents via 
wild birds. 
For this study, the researchers chose northern pintails 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. 
In addition to the samples from more than 1,400 ducks, the scientists 
utilized satellite telemetry in their research. In February 2007, 
biologists from the Alaska Science Center worked with Japanese scientists 
to mark 27 northern pintail ducks with satellite transmitters at Lakes 
Izunuma-Uchinuma in the Miyagi Prefecture of Japan. In February 2008, this 
international research team marked 52 pintails with satellite 
transmitters. Pintails were again marked at Lake Izunuma-Uchinuma as well 
as at Gosho Reservoir in the Iwate Prefecture. An additional sample of 
pintails will be marked in 2009, the final year of the study. 
"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. 
"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, said Pearce. 
The study is published this week in the journal "Molecular Ecology."





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