For the virulent H5N1 strain of avian flu to establish itself on U.S. soil via wild birds, a string of events must come together, none of which can be predicted, according to experts at Cornell's Lab of Ornithology.

They are part of a new avian influenza task force at the lab, intent on understanding, tracking and relaying accurate information to the public about avian influenzas.

While infection by the H5N1 strain of flu is rare in humans, it quickly kills half of those infected. In poultry, the highly pathogenic virus can be extremely deadly, killing more than 90 percent of infected birds within 48 hours. But many wild birds, especially certain waterfowl, can carry the deadly virus in their intestines with few symptoms.

Experts believe wild birds from Asia -- where the disease is widespread among free-flying birds and where the majority of the more than 100 human deaths globally have occurred -- will bring the highly pathogenic H5N1 to the United States, possibly this year. Still, nobody knows which species of birds are capable of flying thousands of miles across the ocean after contracting the disease. Right now, a government task force has its eye on Alaska, where about 30 species of migratory birds, including Arctic warblers and yellow wagtails, will breed this spring after wintering in Asia. The government's task force plans to sample thousands of birds for H5N1 as part of an early detection program.

It is highly unlikely, lab experts say, that a bird would fly from Asia to Alaska and then to the lower 48 states. The fear, however, is that later this summer an infected bird from Asia could mingle with birds from the lower 48 states and Central and South America that also breed in Alaska, like snow geese, common eiders and tundra swans. If that were to occur, a bird could return to the lower 48 states with the deadly virus and hypothetically infect other birds.

But even if the virus did arrive, the chance of wild birds infecting people (who rarely contract the disease in its present form) or poultry (protected by very stringent industry standards and lack of contact with wild birds) is slim.

"If avian flu were to show up in U.S. poultry, migratory birds are probably the least likely source of infection," said Ken Rosenberg, director of conservation science at the Cornell Lab of Ornithology.

"It's a whole lot easier to see someone smuggling an infected gamecock or parrot into the U.S. through Mexico or Canada," added Kevin McGowan, a research associate at the lab, noting that all birds that are sold are regularly exposed to other birds from all over the world in both illegal and legal bird markets.

The Cornell ornithologists, however, point out that bird migration routes are "leaky" -- they are broad pathways rather than narrow streets, and birds regularly get lost. Birds from Asia that breed in Alaska could be found elsewhere, such as along the U.S. Pacific coast. But even if an infected bird landed in the lower 48 states, the poultry industry is probably safe.

"At present there are still no thoroughly documented records of wild birds infecting domestic poultry or humans anywhere," said McGowan.

Highly pathogenic H5N1 appears to have mostly spread in Asia through unregulated movement, trade and handling of infected poultry.

While the researchers are less concerned about avian flu impacting humans or domestic poultry, they point out that the virulence of the highly pathogenic H5N1 creates a real danger to threatened or endangered bird species. Whooping cranes and such species related to poultry as prairie chickens, grouse and quail are all in trouble and could be some of the most susceptible species to the highly pathogenic avian flu.