The Federal Government has sent for testing samples from 14 persons, including three who are dead, for possible bird flu.
Samples from a mother and daughter who died in Lagos and a woman who died in Taraba State after suffering flu-like symptoms are being tested to determine whether the H5N1 strain of bird flu was present.
However, preliminary reports from the World Health Organisation on Monday showed that initial tests on the samples were negative.
But a WHO official said in Geneva that all 14 samples had tested negative for the H5 strain of flu but positive for another type.
According to Dr. David Olaleye, a WHO doctor taking part in the testing at a laboratory in Abuja,
the samples would be sent to a reference laboratory in London for more checks.
�We have done two rounds of tests over the weekend and those were negative … Today we are re-running another round of tests and I am waiting for the results,� he said.
He added that arrangements had been made to transport the samples to the London laboratory on Tuesday.
Samples have been taken from three people who died of unknown causes and 11 people who came into contact with them.
Abdulsalam Nasidi, in charge of efforts to prevent bird flu from spreading to humans in Nigeria, said the three who died had tested positive for flu, which is common at this time of year due to the seasonal harmattan wind.
�The tests will show if it was common flu or bird flu,� Nasidi said.
The other 11 samples are from people who came into contact with those who died.
Nigeria was the first country on the continent to detect bird flu a year ago. The virus has spread to 17 of the 36 states but no human case had been confirmed so far.
It is also one of three countries regarded by experts as the weakest areas in the global attempt to stem infections among birds.
The disease was first discovered in Kaduna a year ago and despite measures such as culling, quarantine and a transport ban on live birds it spread quickly across the country.
Millions of Nigerians keep live poultry in their backyards and in the absence of refrigerators in most households, birds are transported and sold live and killed just before eating.
Bird flu has killed at least 163 people around the world, according to the most recent figures from the WHO. There are fears it could spark a pandemic in which millions could die if it mutates into a form that passes easily from person to person.
Experts have warned that surveillance in Nigeria may not be completely effective because of poor health services.