ABUJA, Nigeria — In an ominous warning as fatalities mounted in West Africa from the worst known outbreak of the Ebola virus, the head of the World Health Organization said on Friday that the disease was moving faster than efforts to curb it, with potentially catastrophic consequences, including a “high risk” that it will spread.
The assessment was among the most dire since the outbreak was identified in March. The outbreak has been blamed for the deaths of 729 people, according to W.H.O. figures, and has left over 1,300 people with confirmed or suspected infections.
Dr. Margaret Chan, the W.H.O. director general, was speaking as she met with the leaders of the three most affected countries — Guinea, Liberia and Sierra Leone — in Conakry, the Guinean capital, for the introduction of a $100 million plan to deploy hundreds more medical professionals in support of overstretched regional and international health workers.
“This meeting must mark a turning point in the outbreak response,” Dr. Chan said, according to a W.H.O. transcript of her remarks. “If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives but also severe socioeconomic disruption and a high risk of spread to other countries.”
She said the outbreak was “caused by the most lethal strain in the family of Ebola viruses.”
The gathering in Conakry came a day after West African leaders seemed to quicken the pace of efforts to combat the disease, in what some analysts depicted as a belated acknowledgment that the response so far had been inadequate.
Before the meeting started, there were indications of discord. The leader of Guinea’s Ebola task force said that emergency measures in Liberia, where schools have been closed, and Sierra Leone could set back efforts to control the worst outbreak of the virus since it was identified almost four decades ago.
“Currently, some measures taken by our neighbors could make the fight against Ebola even harder,” Aboubacar Sidiki Diakité, the Ebola task force leader, told Reuters. “When children are not supervised, they can go anywhere and make the problem worse. It is part of what we will be talking about.”
Sierra Leone’s emergency measures include house-to-house searches for infected people and the deployment of the army and the police.
One person, traveling from Liberia, died in Nigeria, Africa’s most populous nation, which introduced airport screening of travelers from the stricken region on Thursday.
Dr. Chan said that the virus seemed to be spreading in ways never seen before.
“It is taking place in areas with fluid population movements over porous borders, and it has demonstrated its ability to spread via air travel,” she said.
Making matters worse, health workers have been hit particularly hard. Top doctors in Sierra Leone and Liberia have died, and two American aid workers have contracted Ebola and were due to be flown back to the United States for further treatment at Emory University in Atlanta.
The two Americans will be flown in a private air ambulance specially equipped to isolate patients with infectious diseases. The first patient is expected to arrive as soon as Saturday, an Emory spokeswoman said.
“We feel that we have the environment and expertise to safely care for these patients and offer them the maximum opportunity for recovery from these infections,” said Dr. Bruce S. Ribner, an infectious disease specialist at Emory, in a news conference on Friday.
According to the W.H.O., the $100 million plan “identifies the need for several hundred more personnel to be deployed in affected countries to supplement overstretched treatment facilities.”
Hundreds of international aid workers and W.H.O. specialists “are already supporting national and regional response efforts,” the statement said. “But more are urgently required. Of greatest need are clinical doctors and nurses, epidemiologists, social mobilization experts, logisticians and data managers.”
As the alarm about the outbreak has grown, so, too, have concerns that the disease will be carried farther afield by travelers from the stricken countries, despite official efforts to tamp down such fears. The African Union, for instance, announced on Friday that it was postponing a routine rotation of its peacekeeping force in Somalia for fear that new soldiers arriving from Sierra Leone could be infected.
The Philippines said Friday that it would screen travelers from Guinea, Sierra Leone and Liberia when they arrived and monitor them for a month. Lebanon was reported to have suspended work permits for residents of the same three countries, news reports said. Emirates, an airline based in Dubai, said it was suspending flights to Conakry as of Saturday.
At the Commonwealth Games in Glasgow, Moses Sesay, a cyclist from Sierra Leone, told the British tabloid The Daily Mirror that he had been quarantined for four days and tested for Ebola after feeling ill. He has since been pronounced healthy.
“I was sick. I felt tired and listless,” he said. “All the doctors were in special suits to treat me — they dressed like I had Ebola. I was very scared.”
Jackie Brock-Doyle, a spokeswoman for the games, told reporters on Friday: “Just to be really clear, there is no Ebola in the athletes’ village. There is no Ebola virus in Scotland.”
Only weeks after the beginning of the outbreak, the Italian authorities tightened health checks at airports and on ships from West Africa. But epidemiologists in Italy suggested there was little risk that the hundreds of unauthorized migrants who reach southern Italy every day were carrying the virus.
“Migrants cross the desert in journeys that take weeks, if not months, before getting on a boat to Europe,” Dr. Massimo Galli, a specialist in infectious diseases at the University of Milan, said in a telephone interview. “They would manifest the disease long before arriving.”
Adam Nossiter reported from Abuja, and Alan Cowell from London. Gaia Pianigiani contributed reporting from Rome, Alan Blinder from Atlanta, and Denise Grady from New York.