Cameroon became the fourth African country to be struck by the deadly bird flu virus, as the government announced its first confirmed avian case on Sunday.

The H5N1 strain was detected in a duck on a farm outside the northern town of Maroua, near the border with Nigeria, the government said.

The fatal virus was first discovered in Africa on a commercial poultry farm in Nigeria in February. It has since been reported in Niger and Egypt.

Experts have expressed concern that bird flu was likely to be spreading undetected in Africa, which is ill-prepared to deal with the virus and lacks laboratories to detect it.

Cameroon's government said the tests that confirmed the H5N1 strain were carried out in a laboratory in Paris.

Minister of Livestock Aboubakary Sarki told reporters the infected duck was among 10 birds that died in Maroua from Feb. 12-26. He said the government had already slaughtered birds in the area as a precaution, but did not say how many.

Sarki said the government needed help from international donors to vaccinate some 2 million birds and had recently trained 700 veterinarians to vaccinate birds or destroy them.

Sarki said the government had banned the sale of chicken in the affected area, but some residents contacted by phone said it was still being sold.

Cameroon also said it was reinforcing a ban on poultry imports from Nigeria and any other country affected by bird flu. Authorities imposed the ban shortly after the fatal strain was reported in Nigeria.

The H5N1 strain of bird flu has killed or forced the slaughter of more than 140 million chickens and ducks across Asia since 2003, and has recently spread to Europe, Africa and the Middle East. Health officials fear H5N1 could evolve into a virus that can be transmitted easily between people and become a global pandemic.

At least 97 people have died from the disease worldwide, two-thirds of them in Indonesia and Vietnam, according to the World Health Organization. No human cases have been detected in Africa.

Humans and poultry live close together on small farms across Africa, as in Asia where the current H5N1 wave began and where the virus first jumped to humans.