Nigeria has recorded its second Ebola case - that of one of the doctors who treated a man who died from the virus after his arrival from Liberia.
The health minister said a further eight people who came into contact with him have been placed in quarantine.
This year's outbreak, the worst ever, has centred on Guinea, Liberia and Sierra Leone, killing 887 people.
New figures from the UN show that between 31 July and 1 August, 61 deaths were reported.
Meanwhile, Liberia has ordered that the bodies of people killed by the Ebola virus must be cremated following the refusal of some communities to allow the burial of Ebola victims on their land.
The virus spreads by contact with infected blood and bodily fluids - and touching the body of someone who has died of Ebola is particularly dangerous.
Health experts say burial ceremonies have played a role in the transmission of the virus.
The evacuation of the second US health worker to become infected in Liberia is expected early on Tuesday morning.
Nancy Writebol will be flown to Atlanta in the US to a special isolation ward at Emory University Hospital, where Dr Kent Brantly, who arrived from Liberia on Saturday, is being treated by infectious disease specialists.
Nigeria's Health Minister Onyebuchi Chukwu said that in total 70 people were traced who had come into contact with the man who died there, Patrick Sawyer.
Sawyer, an employee of the Liberian finance ministry, had arrived by plane in Nigeria, Africa's most populous country, from Monrovia after changing planes in Togo's capital, Lome, on 20 July.
He was immediately taken to hospital in Lagos and died five days later in quarantine.
Ebola virus disease (EVD)
- Symptoms include high fever, bleeding and central nervous system damage
- Fatality rate can reach 90%
- Incubation period is two to 21 days
- There is no vaccine or cure
- Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
- Fruit bats are considered to be virus' natural host
On Friday, Margaret Chan, head of the World Health Organization, met the leaders of Guinea, Liberia and Sierra Leone to launch a new $100m (£59m) Ebola response plan.
According to the UN, more than 60 of the Ebola deaths so far have been health care workers.
There is no cure or vaccine for Ebola - but patients have a better chance of survival if they receive early treatment.
The current outbreak is killing between 50% and 60% of people infected.
Initial flu-like symptoms can lead to external haemorrhaging from areas like eyes and gums, and internal bleeding which can lead to organ failure.
In Sierra Leone, the army is in the process of deploying about 750 troops to the east of the country to help health officials quarantine areas affected by Ebola.
Code-named Operation Octopus, the deployment, which includes military doctors and nurses, began on Sunday and is expected to take three days.
Meanwhile, Sierra Leoneans did not go to work on Monday and the capital, Freetown, is eerily quiet, the BBC's Umara Fofana reports from the city.
They are observing a "national stay-at-home day" called by the president so that all citizens can pray to help end the crisis and educate one another about the disease, he says.
And the country's football association has suspended all football matches because of the outbreak until further notice.
According to new UN figures on the West Africa Ebola outbreak, over two days last week, there were 13 new cases reported in Guinea, 77 in Liberia, and 72 cases in Sierra Leone.