The number of Ebola cases has passed 10,000, according to the World Health Organisation, as the outbreak continues to spread.
Authorities in Mali were scrambling to contain fears on Saturday after the death of a two-year-old girl who had travelled 700 miles on the country’s bus network before receiving treatment.
And in the US, President Barack also tried to reassure a panicking public after two states imposed compulsory quarantine for doctors and nurses arriving home after treating patients overseas.
The WHO says the number of cases is continuing to grow exponentially in Guinea, Liberia, and Sierra Leone.
On Saturday it revealed its latest statistics, which put the total at 10,141. Of those, 4,922 people had died.
The United Nations health arm has said repeatedly that even those figures are likely to underestimate the true scale of the outbreak as many people have been unable or too frightened to seek medical care.
Four WHO experts are on their way to Mali – the sixth West African country to record an Ebola case – to reinforce its team there this weekend.
Markatche Daou, a spokesman for the Malian ministry of health, said the girl had arrived from Guinea where she had visited Kissidougou, the town where the outbreak was first identified in December last year.
“Everyone who had contact with the girl is under medical surveillance,” he said.
The WHO warned that many people in Mali had potentially been exposed to the virus because the toddler travelled across the country while she displayed symptoms. More than 40 people with whom she was in contact, including 10 health care workers, are being monitored for symptoms that include fever.
The current outbreak is the worst in history.
So far only 27 cases have occurred outside the most badly hit three countries. However, the WHO has identified 15 other African nations it fears are at high risk of importing the disease.
But there was one optimistic note in its latest update: trials of vaccines could begin in West Africa in December, earlier than expected, and hundreds of thousands of doses should be available for use by the middle of next year.
Meanwhile, authorities in New York have begun disinfecting bars and restaurants visited by Craig Spencer, a 33-year-old doctor, who tested positive for the disease on Thursday night.
The case sparked anxiety among New Yorkers, who complained that Dr Spencer should have been quarantined on returning from Guinea where he had been treating Ebola patients with the medical charity Medecins Sans Frontieres.
Biohazard teams have cleaned Dr Spencer’s apartment and a bowling alley he visited shortly before being taken ill.
Friends said he was well enough to talk to them by telephone and had been able to practise yoga in his hospital room.
They have been forced to defend his actions after criticism that he should not have been allowed to travel freely after returning home.
However, Dr Mary Travis Bassett, the city health commissioner, defended his actions, pointing out that he had quarantined himself as soon as he displayed symptoms.
“There’s this young guy who went over there, really doing the right thing, the courageous thing, and he handled himself really well,” she told The New York Times. “I don’t want anyone portraying him as reckless.”
Also on Saturday, health officials in New Jersey said a nurse who developed a fever on Friday after returning from West Africa had tested negative for Ebola.
She was the first person to be quarantined on arrival at a US airport, following tough new rules introduced in New York and New Jersey.
They were imposed amid criticism that Washington was not doing enough to prevent the disease being carried into the US and calls for a complete ban on passengers arriving from West Africa.
Andrew Cuomo, governor of New York, said: “A voluntary Ebola quarantine is not enough. This is too serious a public health situation to leave to the honour system of compliance.
“I think increasing the screening procedures is necessary and reduces the risk to New Yorkers and people in New Jersey.”
Health workers who have been in contact with Ebola patients now face 21 days in isolation wards when they arrive back in the two states.
President Barack Obama used his weekly Saturday address to reassure Americans. He said the disease was difficult to catch and that all seven Americans who had contracted Ebola had been treated successfully.
“And we have to be guided by the science — we have to be guided by the facts, not fear,” he said. “Yesterday, New Yorkers showed us the way.
“They did what they do every day — jumping on buses, riding the subway, crowding into elevators, heading into work, gathering in parks.
“That spirit — that determination to carry on — is part of what makes New York one of the great cities in the world. And that’s the spirit all of us can draw upon, as Americans, as we meet this challenge together.”