Doctors have begun screening workers in northern Nigeria at the first poultry farm to be confirmed with the deadly bird flu virus in Africa.
None of the workers has shown signs of illness yet
The virulent H5N1 strain was found in birds in three states last week. Health Minister Eyitayo Lambo said another five states had suspected cases.
Some farmers are angered by the government's handling of the outbreak, saying compensation was too low.
Thousands of chickens have been dying in Nigeria for more than a month.
No humans have tested positive for the virus in Nigeria but there are fears that the emergency measures may have come too late to stop the virus spreading.
Dr Mohammed Bala Abubakar, from Kaduna State's health ministry, told the BBC that tests were being carried out on some 120 workers from Sambawa farm in Kaduna State on Monday and would continue throughout the week.
None of the workers on the farm where the outbreak was first identified have shown any signs of illness, he said.
Two children, who live near the farm in Kaduna State and who fell ill last week, have since recovered and been released.
Their blood samples have been sent to several laboratories for analysis, he said.
H5N1 has also been found on farms in Kano and Plateau States, either side of Kaduna.
Mr Lambo and his health ministry officials say there are five other states with suspected bird flu cases: Abuja, where the capital is located, Katsina, Nassarawa, Yobe and Jigawa states.
Experts with protective equipment are being flown in from abroad to help local officials contain the spread of the disease.
Neighbouring countries have banned chicken imports from Nigeria.
Meanwhile, farmers in Kano, who estimate they have lost some 150,000 chickens since the crisis began, are demanding $10 in compensation for each bird lost.
So far, the government has only offered them $2 for each chicken.
The BBC's Ado Saleh in Kano says there is a rising sense of panic among the farmers as they have yet to be told what has been killing their livestock.
People have rushed to sell poultry at market before restrictions bite
The World Health Organization (WHO) has called for a massive public education campaign, to stop bird flu from spreading to humans in Nigeria.
It is not clear how the virus has spread to Nigeria. It was first found in South-East Asia and more recently Turkey and Russia.
Some experts blame illegal poultry imports; others migrating birds.
More than 80 people have died of H5N1 bird flu since the disease's resurgence in December 2003 - most of them in South-East Asia.
Experts point out that cross-infection to humans is still relatively rare, and usually occurs where people have been in close contact with infected birds.
But they say if the H5N1 strain mutates so it can be passed between humans, it could become a global pandemic, killing millions.