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The U.S. researchers from the University of Georgia reported Tuesday they have found that the common wood duck and laughing gull are very susceptible to highly pathogenic H5N1 avian influenza viruses and have the potential to transmit them.

 

Their finding, published in the November issue of the journal Emerging Infectious Diseases, demonstrates that different species of North American birds would respond very differently if infected with these viruses. David Stallknecht, associate professor of the UGA College of Veterinary Medicine and co-author of the study, said knowing which species are likely to be affected by H5N1 viruses is a vital component of efforts to quickly detect the disease should it arrive in North America.

 

"If you're looking for highly pathogenic H5N1 in wild birds, it would really pay to investigate any wood duck deaths because they seem to be highly susceptible, as are laughing gulls," said Stallknecht. "It was also very interesting that in some species that you normally think of as influenza reservoirs -- the mallard, for instance -- the duration and extent of viral shedding is relatively low. This may be good news since it suggests that highly pathogenic H5N1 may have a difficult time surviving in North American wild birds even if it did arrive here."

 

Working under controlled conditions in an airtight bio-security lab of Department of Agriculture, the researchers determined how much of the virus was shed in the feces and through the respiratory system of several species of wild birds."We chose birds that, because of their behavior or habitat utilization, are most likely to transmit the virus or bring the virus here to North America," said lead author and doctoral student Dr. Justin Brown.

 

The species studied were: mallards, which are often infected with commonly circulating, low-pathogenic avian influenza viruses in North America and Eurasia; northern pintails and blue-winged teal, which migrate long distances between continents; redheads, a diving species; and wood ducks, which breed in northern and southern areas of the United States. The laughing gull is a common coastal species ranging from the Southern Atlantic to the Gulf Coast. Stallknecht explained that in low-pathogenic avian influenza, most of the virus is shed in the feces of birds. The virus then spreads as other birds drink from contaminated water. The study found that in highly pathogenic H5N1 avian influenza, however, the birds shed most of the virus through their respiratory tract.

 

Stallknecht said with this knowledge, scientists can more effectively detect the virus in live birds by swabbing the birds' mouths and throats.

 

"Doing avian influenza surveillance is pretty tricky because there are a lot of species differences and there are also seasonal differences," he said. "So you've got to pick the right species at the right time and you've got to collect the right samples."

 

(Xinhua News Agency October 25, 2006)