"But the big question is, How much of our knowledge about these viruses can we translate to high-pathogenic viruses" such as the H5N1 strain of bird flu?
In poultry avian viruses can mutate into more virulent influenza strains, including H5N1.
If this mutated virus then finds its way back into wild populations, the birds could then spread the disease through migration.
Some scientists have argued that wild birds infected with HN51 would be too ill to migrate. Swans, for instance, appear to be particularly vulnerable to the strain.
"Swans apparently drop dead quite easily, but they are unlikely to be the vector because they are not going to fly very far if they are dead," Fouchier said.
But the study team says that some birds that have been purposely infected for the sake of research show that wild birds can survive H5N1.
"For some reason H5N1 has adapted so it no longer kills dabbling ducks," Fouchier said.
This means the ducks may be able to spread the virus over a wide area.
The study team says migratory geese may also be vectors, because they often graze in huge flocks, a practice that could encourage transmission.
Migrating ducks, the researchers add, "could provide an intercontinental bridge" for bird flu to North America, which has not yet had any known cases of H5N1. (See "Bird Flu Will Reach U.S. and Canada This Fall, Experts Predict.")
No Wild Culls Needed?
However, there is currently no reason to cull wild birds to control the spread of H5N1, the study says.
Wild birds, though, should be kept away from poultry, the researchers say.
"For all of the outbreaks that have ever been recorded for bird flu, it's clear that the poultry-production industry itself is responsible for most of the spread through poultry trade [and the] movement of people and equipment between farms," Fouchier said.
"You can prevent your chickens and turkeys from getting into contact with wild birds by simple biosecurity measures" such as keeping farm birds enclosed, he added (photo: "Ducks in Detention").
BirdLife International, a global bird-conservation group based in Cambridge, England, says culling operations may in fact spread the virus to noninfected areas by forcing diseased birds to disperse.
Last week Shafqat Kakakhel of the United Nations Environment Programme spoke at a conference on bird flu and migratory birds in Nairobi, Kenya.
"Blaming avian flu on bird migrations is misleading. And a 'quick fix' of culling migratory birds is certainly not the solution," Kakakhel said.
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