A top U.N. health official has declared a regional bird flu crisis in West Africa, centered in Nigeria and Niger.The official predicts the virus will jump to North America within months.

Dr. David Nabarro, the U.N. Coordinator for Avian and Human Influenza says the spread of the H5N1 strain of bird flu has reached disturbing proportions in some parts of Western Africa. He says the entire region is at risk.

"We are truly focusing on Africa," said David Nabarro. "There is a regional crisis in West Africa associated with H5N1. Two countries are affected, Nigeria and Niger, but we are frankly anticipating that we will find the virus in other West African countries, and there's a lot of preparatory work underway."

Dr. Nabarro said West Africa is a special challenge because much of the population lives on less than $1 a day, with backyard poultry a big source of income. He said helping the region's impoverished residents is difficult because few can afford the chicken coops that would help to contain the spread of the virus.

There are no reported human cases of the H5N1 flu strain in Nigeria, but the U.N. official noted a recent outbreak in China, where a nine-year old girl died. He said he is also keeping Egypt, Indonesia and Russia under close review

Dr. Nabarro said cases are popping up in new places as birds migrate. He predicted that as flocks of birds travel north from West Africa on a flyway that takes them across the Arctic Circle and on to North America, it is only a matter of months before the virus shows up in the United States.

"So we're obviously anticipating that there will be H5N1 in birds moving back north up that West Africa Atlantic flyway in the not too distant future," he said. "And so we would then anticipate that. There will be movement south into the Americas of birds that have intermingled. So it's certainly within the next six to 12 months, and who knows, it may be earlier.

Dr. Nabarro urged national governments to put their veterinary services on high alert for avian flu, to try to ensure they are not caught unaware if the virus hits local poultry populations.

The H5N1 strain of flu has led to the deaths of millions of birds in more than 30 countries. More than 170 human cases have been reported since 2003, 96 of them fatal.

Human cases are rare, but authorities fear the avian flu will mutate into a form than can be transmitted from person to person, touching off a pandemic that could kill millions of people.

U.S. officials say they are planning to test as many as 100,000 birds for the virus this year, most of them in Alaska and the Pacific islands where migrating birds from Asia and North America cross paths.