"If the situation in Nigeria gets out of control, it will have a devastating impact on the poultry population in the region, it will seriously damage the livelihoods of millions of people and it will increase the exposure of humans to the virus,

Nigeria's Agriculture Minister Adumu Bello confirmed findings by the Paris-based World Organization for Animal Health, known as the OIE, of an outbreak of the H5N1 virus on a poultry farm in the northern Nigeria state of Kaduna. No human infections were reported, but 40,000 birds died of bird flu, according to OIE.

The farm had a total of 46,000 chicken, geese and ostriches, and all those that escaped bird flu were destroyed, OIE said. Nigeria ordered the quarantine and culling of any fowl suspected of carrying bird flu in hopes of halting its spread in Nigeria, officials said.

"The significance is that it's a completely new continent that we need to be looking at," Alex Thiermann, an expert for the World Organization for Animal Health, said of H5N1's arrival on the world's poorest continent.

Serious Damage to Livelihoods

Experts are concerned that H5N1, which has caused human as well as bird deaths in Asia and spread to Europe and the Middle East, might mutate into a form spread easily among humans, triggering a pandemic that could kill millions. So far, H5N1 has passed only from birds to humans, not from human to human.

The Chinese government said Wednesday a 26-year-old Chinese woman has contracted bird flu, becoming at least the 11th person to be infected with the disease in China.

Sub-Saharan Africa, with about 600 million of the world's poorest people, is particularly ill-equipped to deal with a major health crisis. With weak and impoverished government institutions in regions where many people keep chickens for badly needed food, experts say any mass killings of the animals -- often a first step in controlling bird flu -- will be difficult to pull off.

Thiermann noted that some African countries have "very weak" veterinary systems.

"It is absolutely essential to strengthen the veterinary infrastructures in order to have the capability for early detection and a rapid response," he said.

The World Health Organization said Nigeria has a poultry population of about 140 million and that the country's overtaxed veterinary services needed international help, while calling on other African countries act quickly against any suspected outbreaks.

"If the situation in Nigeria gets out of control, it will have a devastating impact on the poultry population in the region, it will seriously damage the livelihoods of millions of people and it will increase the exposure of humans to the virus," said Samuel Jutzi, head of the UN Food and Agriculture Organization's Animal Production and Health Division.

"It is important that local and national authorities within other countries in the region remain vigilant for possible outbreaks of suspected avian influenza in poultry and other birds," he said in a statement.

More Help Is Needed

Two other west African nations -- Gabon and Mauritania -- imposed measures Wednesday to fight against any outbreaks in those countries.

Nigeria, Africa's most-populous nation with 130 million people, said it would work to halt the flow of any sick birds into uninfected zones.

"We shall quarantine and stamp out all livestock in any farm suspected of having avian influenza and pay full compensation to the owners," said Bello, the minister. "We shall impose restrictions on movements in any suspected [area] and conduct the necessary tests."

Thiermann said that was a good start. He said a team of experts will head to Nigeria later in the week to assess and provide technical advice, but more is needed.

"We feel that they are doing everything they can and they certainly need help," he said of Nigeria.

In Kano, next to the state where the H5N1 strain was found, officials said Wednesday that first tests taken from among 60,000 dead birds there showed no signs of bird flu. But market sellers in the regional capital of Kano quickly halved prices on chickens they brought to market, and some said birds were still being moved around the region.

Awalu Haruna, secretary of the Poultry Farmers' Association of Kano, accused the government of being slow to respond to the epidemic of poultry deaths in the state.

"The government should have quarantined the affected farms to prevent further spread," he said. "But as I speak this has not been done. There is still movement of humans and birds in and out of these farms."

The samples that showed bird flu in Kaduna state were sent for testing in Italy after being taken Jan. 16 on the farm that raises eggs for consumption.

Thiermann said it wasn't known how the bird flu virus entered Nigeria, but said migratory waterfowl likely played a role. No cases of bird flu have yet been reported elsewhere in Africa.

Bird flu began ravaging poultry stocks across Asia in 2003, forcing the slaughter of 140 million birds and jumping to humans, killing dozens.

Associated Press writers John Leicester in Paris and Oloche Samuel in Kano, Nigeria, contributed to this report.