World veterinary experts on Wednesday raced to help Nigeria attempt to contain a bird-flu outbreak in the north of the country, as the arrival of the deadly H5N1 virus in Africa was confirmed.

Its appearance on the world's poorest continent, where veterinary controls are often weak and health systems are stretched by lack of funds and epidemics such as HIV/Aids, has long been feared, given the potential for the disease to spread from infected birds to humans.

Many people live in close proximity to poultry, just as in South-East Asia where H5N1 has cut a swathe through domesticated flocks and caused scores of deaths since it emerged late in 2003. Chicken is the main, and often only, source of protein and there are fears that owners might be reluctant to report disease.

European authorities are already assessing the risk from migratory birds making the journey north from West Africa this spring, although how big a factor migration is in spreading the disease is disputed. Movements of poultry, traded exotic and other birds and of people are all possible factors.

The highly pathogenic virus strain found in Nigeria -- which was confirmed by tests in Padua, Italy -- is said to be similar to those that have been found in birds in Siberia and Mongolia, and further tests are under way to determine how close the Nigerian samples are to the H5N1 detected in other parts of the world.

In London, the Department for the Environment (Defra) claimed that while the risk of a further global spread of avian flu is high, the chances of it arriving in Britain remain low, although assessments are being reviewed.

The news of the Nigerian outbreak, at a large farm in Jaji, in the state of Kaduna, coincided with fears that bird flu is now spreading through Iraq. The avian virus, which has already claimed the life of a teenager in the largely autonomous region of Kurdistan, is now being investigated as the possible cause of death of a pigeon-seller in the southern city of Amara. Worldwide, 88 of the 165 people confirmed as being infected with the avian virus have died.

The threat remains that the virus will mutate further into something that can spread easily between people and kill millions.

Samples were taken from the Nigerian farm, which is home to chicken, geese and ostriches, on January 16. The owner had treated birds with antibiotics before the flu was confirmed. Of 46 000 birds on the farm, 40 000 had died.

The World Organisation for Animal Health (OIE) said it will take immediate action and a team of experts is being sent to the affected area to help the national authorities.

Alex Thiermann, one of the experts, said: "The significance is that it's a completely new continent we are looking at." He commended the quick response of the Nigerian authorities, including culling, quarantine, controls on animal movement and disinfection, but noted that the country is on a major migration flyway.

In Ghana, separated from Nigeria by Togo and Benin, authorities said they are on full alert, doing random surveys and keeping an eye on wild wetland birds. Samples from wild waterfowl in Malawi, Sudan and Kenya will soon be tested at the Onderstepoort Veterinary Institute in South Africa, the main testing site for avian flu in Africa.

Wild birds do carry avian flu, of which there are 144 types, but a spokesperson for the Royal Society for the Protection of Birds warned against jumping to conclusions. If the strain was carried by birds migrating from parts of Europe already hit by the disease, the outbreak would more likely have taken place in the east of the continent. Andre Farrar said: "Teasing out what is underlying the movement of the virus is proving a challenge, but it is all too easy a shorthand that migrating birds spread it around.

"The concern is about ducks, geese and swans, which don't go from the United Kingdom to Africa and back again. Waterfowl wintering in Britain clear off in March/April and are replaced by summer migrants, swallows and little things that are not going to be a primary concern to moving H5N1. They are more or less irrelevant in terms of risk to humans and poultry."

Checks on more than 3 000 wild birds in Britain during the autumn have revealed three cases of low pathogenic avian flu, not of the H5N1 variety.

An assessment by Defra experts three weeks ago concluded: "Preliminary discussions indicate that there is not much reliable information on bird migration or mixing within Africa. It is, however, reasonable to expect that birds will follow established routes: that is, birds that have migrated to East Africa will return over Eastern Europe to their breeding grounds in southern Siberia, while the birds from West Africa will return over the Mediterranean basin to their breeding grounds in north Russia.

"It is, however, unlikely that a substantial number of migratory birds would come directly from West Africa to the UK."