for National Geographic News
Wild ducks and other migratory birds could be important carriers of deadly bird flu, researchers say.
Even so, the infectious-disease experts say there is no solid basis for killing wild birds to protect poultry and minimize the risk of human infection.
The European team investigating the global spread of the H5N1 strain of avian influenza says certain duck species may be infecting wild bird populations.
Geese and wading birds are also possible vectors of the virus, the team says.
The team's study, to be published tomorrow in the journal Science, was led by Björn Olsen of Umeå University in Sweden. Olsen runs Europe's largest wild-bird flu-monitoring program.
Studies have shown that influenza viruses in lake water, generally passed via bird feces, can stay infectious for up to 30 days.
The migration or feeding behavior of dabbling ducks could at least partially explain the spread of the H5N1 strain of bird flu, the researchers add.
This group of duck species includes mallards, teal, pintails, and others that feed at or near the surface, where viruses in water are most likely to be picked up.
Perhaps as a result, dabblers have the highest known rates of avian influenza infection, the study says. For instance, nearly 13 percent of mallards tested positive for bird flu. Other species tested include the American black duck (18.1 percent), blue-winged teal (11.5 percent), and northern pintail (11.2 percent).
However, bird flu viruses appear to exist in ducks in a low-pathogenic form, meaning infection doesn't usually lead to severe illness and death.
"Dabbling ducks are for sure the prime hosts for low pathogenic viruses," said study co-author Ron Fouchier, a virologist at the Erasmus Medical Center in Rotterdam, Netherlands.
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