The World Health Organisation has warned that bird flu is likely to be detected in other African countries after a case of the deadly H5N1 strain was discovered in pourltry in Nigeria yesterday.
Dr David Nabarro of the WHO said the virus might be "quite widespread".
"If it's in Nigeria it might also be in other countries that are less well-equipped," he told the BBC in an interview.
Samuel Jutzi of the UN's Food and Agriculture Organisation
"We've got to have all countries, particularly in West Africa, being very vigilant for bird die-offs, which are the indicator of bird flu being in the population," he added.
The outbreak in Nigeria opens a fresh front in the battle against the virus, which has killed at least 88 people in seven countries since it reemerged in late 2003. War-ravaged Iraq is also struggling to contain the disease.
"The outbreak in Kaduna state in northern Nigeria proves that no country is risk-free and that we are facing a serious international crisis," said Samuel Jutzi, a director of the UN's Food and Agriculture Organisation (FAO) in Rome.
"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," Mr Jutzi added.
Nigerian Agriculture Minister Adamu Bello said there had not been any poultry workers infected so far. However, it would be difficult for authorities to know this for sure as mortality rates in impoverished Nigeria are among the highest in the world and people are often buried without any formal medical check.
World Health Organisation (WHO) regional adviser Adamou Yada noted there had not yet been any known cases among humans in Africa. "In Africa we have so many diseases, so many priorities, if it spreads in Africa it will be a nightmare," Mr Yada told Reuters from WHO Africa headquarters in the Congo Republic.
Migratory birds have been blamed for the spread of the virus, but it is not clear how it reached Nigeria, with a poultry population of 140 million. Experts called for urgent action to halt further spread.
"What is most important now is not how it got into Nigeria but how it can be prevented from leaving Nigeria," said Phil Hockey of the Percy FitzPatrick Institute of African Ornithology in Cape Town.
"The prospect of bird flu loose in sub-Saharan Africa is a scary one because of the way that human and domestic bird populations are so closely intermingled," he said.
So far, victims have contracted the disease through close contact with infected birds. Experts stress cases of human infection are relatively few compared with the millions of birds that have contracted the disease.
But scientists fear that H5N1 could mutate into a form that passes easily from person to person, sparking a human influenza pandemic.
Two Indonesian women from an area just east of the capital are in hospital after local tests showed they had the H5N1 bird flu virus, a senior Health Ministry official said today.
In China the latest bird flu patient brought the number of the country's confirmed cases in humans to 11, the Xinhua news agency said. Seven people have died from the virus in China. The patient, a 26-year-old woman farmer from eastern China's Fujian province, was in a stable condition, Xinhua said, citing a report from the Ministry of Health.
Iraq last month became the latest country to suffer a human death from the virus when a teenage girl in the north died.