GENEVA -- The Ebola outbreak in West Africa eventually could exceed 20,000 cases, more than six times as many as are now known, the World Health Organization said Thursday.
A new plan by the U.N. health agency to stop Ebola also assumes that the actual number of cases in many hard-hit areas may be two to four times higher than currently reported. If that's accurate, it suggests there could be up to 12,000 cases already.
"This far outstrips any historic Ebola outbreak in numbers. The largest outbreak in the past was about 400 cases," Dr. Bruce Aylward, WHO's assistant director-general for emergency operations, told reporters.
"What we are seeing today, in contrast to previous Ebola outbreaks: multiple hotspots within these countries - not a single, remote forested area, the kind of environments that have been tackled in the past. And then not multiple hotspots within one country, but international disease."
Another new dimension, he said, is the difficulty of dealing with Ebola in large cities and broad areas.
The agency published new figures saying that 1,552 people have died from the killer virus from among the 3,069 cases reported so far in Liberia, Sierra Leone, Guinea and Nigeria. At least 40 percent of the cases have been identified in the last three weeks, the U.N. health agency said, adding that "the outbreak continues to accelerate."
In Geneva, the agency released a new plan for handling that aims to stop Ebola transmission in affected countries within six to nine months and prevent it from spreading internationally.
The plan calls for $489 million to be spent over the next nine months and requires 750 international workers and 12,000 national workers.
The goal is to take "the heat out of this outbreak" within three months, he said. That will enable WHO to start using classic containment strategies to stop transmission altogether.
The next goal, Aylward said, is to be able to stop transmission within eight weeks of a new case being confirmed anywhere. "That is extremely aggressive but that can be done. It has been done in remote forested areas; it has not been done in urban areas."
The third major goal is to increase the preparedness for dealing with Ebola in all nations that share borders with affected countries or have major transportation hubs, he said.
The 20,000 cases figure, said Aylward, "is a scale that I think has not ever been anticipated in terms of an Ebola outbreak."
"That's not saying we expect 20,000," he added. "But we have got to have a system in place that we can deal with robust numbers."
Air France on Wednesday canceled its flights to Sierra Leone, but Aylward said the agency is urging airlines to lift most of their restrictions about flying to Ebola-hit nations.
"This is absolutely vital," he said. "Right now there is a super risk of the response effort being choked off, being restricted, because we simply cannot get enough seats on enough airplanes to get people in and out, and rotating, to get goods and supplies in and out and rotating, so this is a big part of what has got to be sorted."
Nigerian authorities, meanwhile, said a man who contracted Ebola after coming into contact with a traveler from Liberia had evaded surveillance and infected a doctor in southern Nigeria who later died.
Because of the fear and stigma associated with the virus, health officials say many infected people are trying to conceal their illness and avoid seeking treatment until it is too late. Doctors Without Borders nurse Monia Sayah, who recently returned from working with Ebola patients in Guinea, told CBS News "the fear is palpable." Sayah found that many local communities distrust the healthcare system and foreigners. "Some have said we brought the Ebola to them," she said. "It's very difficult to contain the outbreak when communities are not cooperating."
The announcement of a sixth death in Nigeria marked the first fatality outside the commercial capital of Lagos, where a Liberian-American man, Patrick Sawyer, arrived in late July and later died of Ebola. On Wednesday, Nigerian authorities said they have not yet eliminated the disease from Africa's most populous nation but that it was being contained.
The doctor's wife is in isolation after she started showing symptoms of Ebola, Nigerian Health Minister Onyebuchi Chukwu added. Morticians who embalmed the doctor are part of a group of 70 people now under surveillance in Port Harcourt.
The World Food Program says it is preparing to feed 1.3 million people in Guinea, Liberia and Sierra Leone in the coming months because measures to control an Ebola outbreak have cut off whole communities from markets, pushed up food prices and separated farmers from their fields. Denise Brown, the West Africa regional director for the U.N. agency, said $70 million is needed immediately to meet those needs.
She said the unprecedented challenge of distributing food in an Ebola zone means that the agency is taking longer to reach full capacity.