Migratory patterns will probably take birds carrying the virus from West Africa to the Arctic and Alaska this spring, Dr. David Nabarro said Wednesday. Some infected birds will then likely move south in the fall on a migratory route to the Americas.
"I think it's within the next six to 12 months," Nabarro told a news conference, "And who knows — we've been wrong on other things, it may be earlier."
Meanwhile, a German lab says bird flu has spread to another animal species there.
The lab found the virus in a weasel-like mammal called a stone marten.
The marten was found on a northern German island where an infected cat was found last month. Infected cats have since been found in Austria. Cats are believed to have caught the virus by eating infected birds. A German official notes that martens and cats eat comparable foods.
The H5N1 strain has spread rapidly through Asia and Europe and recently reached Africa, devastating poultry stocks. Virtually all people who have gotten bird flu have had close contact with infected poultry.
In other developments:
Scientists worry that birds arriving in Alaska from Asia may bring in the H5N1 virus and pass it along to other birds, which will fly south this fall.
Scientists will study live birds, others that are found dead or killed by hunters, and environmental samples that might carry the worrisome form of bird flu. While most concern about birds flying south through the United States focuses on their Pacific route in the western states, other migratory paths will be included, Clifford said.
The goal is to test 75,000 to 100,000 live or dead birds this year, said Angela Harless of the USDA. The testing, which also will include some Pacific Ocean islands, will focus on waterfowl and shorebirds.
Human cases are uncommon, but scientists worry that the virus may mutate into a form that can pass easily between people and lead to a worldwide flu epidemic.
Nabarro reiterated the World Health Organization's warning that "there will be a pandemic sooner or later" in humans, perhaps due to H5N1, or perhaps another influenza virus, and it could start any time.
"Because it is moving and because we believe wild birds are implicated, predicting where it's going to flare up next is a very tricky thing to do, and being able to know the scale of the flare-up is also quite tricky," Nabarro said.
Nabarro said the United Nations was focusing on controlling the H5N1 strain in domestic poultry through slaughters and vaccinations. The focus at the moment is on Africa, especially West Africa, where 50 percent of people live on less than $1 a day and many families rely on chickens for their livelihoods, he said.
"There is a regional crisis in West Africa," with outbreaks in Nigeria and Niger, Nabarro said. "But we are frankly anticipating that we will find the virus in other West African countries and there is a lot of preparatory work under way."
In Western Europe, several countries have detected H5N1 in dead wild birds, but there have been few cases in domestic and commercial poultry populations, he said.
One or two cats are also reported to have H5N1, and the WHO says more research is needed on transmission to other mammals, he said.
The U.S. government hopes to test 75,000 to 100,000 live or dead birds this year, a significant increase over past years, with the effort focused on Alaska, according to U.S. Department of Agriculture officials.
"Some of the challenges we face now are really quite dramatic and call for a lot of technical expertise," Nabarro said.
For example, the FAO reported in September that wild birds are able to carry the H5N1 strain while remaining asymptomatic, yet swans in Western Europe are dying from the strain and nobody knows why, he said.
Nabarro said an international conference on wild birds will be held in June and will hopefully include the results of research now under way. The next major international review of global bird flu efforts will also be in June, he said.