In the six months since this outbreak was first formally reported in March, 337 health care workers have been infected, of whom more than 181 have died, WHO said.
A six-month report from WHO -- which assesses the situation in three countries at the outbreak's center, Guinea, Liberia and Sierra Leone -- is dedicated to those health workers "who, as an expression of our innately shared human compassion, risked their lives, and lost them."
A separate nine-month assessment published by WHO experts in The New England Journal of Medicine says the fatality rate of this outbreak in West Africa is 71% and that the "current epidemiologic outlook is bleak."
It warns that without drastic improvements in measures to control its spread, the number of cases and deaths from Ebola is expected to continue climbing from hundreds to thousands per week in the coming months.
Rather than this strain of the virus being particularly virulent, it says, the devastating course of this outbreak seems "likely to be a result of the combination of dysfunctional health systems, international indifference, high population mobility, local customs, densely populated capitals, and lack of trust in authorities after years of armed conflict."
"Perhaps most important, Ebola has reached the point where it could establish itself as an endemic infection because of a highly inadequate and late global response."
It warns that the global response must improve to meet the threat posed by this and future epidemics.
The WHO's six-month report on Guinea, where the outbreak began in a remote area, details how the virus first gained a grip on a vulnerable, frightened population ill-equipped to deal with the deadly disease.
Once Ebola was identified as the killer, a national and international response swung into gear. But each time it looked like the country might be at the point of controlling the virus, new flare-ups occurred.
Some speculated that these were due to the strength of this strain of the virus. But the WHO report concludes it is more likely that Ebola was reintroduced "into Guinea -- with its notoriously porous borders -- from the large outbreaks in neighboring Liberia and Sierra Leone."
That conclusion suggests that controlling the virus in Guinea will not be feasible until its neighbors halt its spread. "On current trends, the prospects that this will happen anytime in the near future are distinctly not good at all," the report said.
Meanwhile, health workers in Guinea have come under attack as they seek to educate the local population.
"Today, one of the biggest barriers to control is violence from an impoverished, terrified and shattered population that does not understand what hit it and fights back the only way it can," the report said.
WHO's six-month report on Liberia summarizes the state of play as one of "misery and despair tempered by some good reasons for hope."
The number of cases there is increasing exponentially, with 113 new ones reported over a single 24-hour period on one day last week, WHO said -- a record number in any outbreak. At the same time, treatment centers are overflowing, and many patients are turned away.
"The true number of deaths will likely never be known, as bodies in the notoriously poor, filthy and overcrowded West Point slum, in the capital, Monrovia, have simply been thrown into the two nearby rivers," the report said.
The capacity to deliver other basic health services, such as care for women in childbirth, has also been badly hit. Some experts estimate that malaria-related deaths may soon surpass those from Ebola, the report warns.
The signs of hope can be found in the opening of a new WHO-funded, 120-bed Ebola treatment center, it said. The U.S. government is also setting up a new laboratory that will speed up diagnosis.
As the Liberian government also works to set up more community care facilities in rural areas, the tide may start to turn.
"Gradual, then likely dramatic, improvements can now be anticipated," the report said.
The situation assessment for Sierra Leone explains how traditional burial practices helped the virus spread quickly there following the funeral of a respected local healer.
The virus has taken a devastating toll on health workers and researchers who've sought to contain its march.
"Sierra Leone's most urgent needs include more treatment beds in much safer facilities, better contact training and follow-up, more personal protective equipment and body bags, and more properly protected teams to collect bodies and bury them safely," WHO said.
The deployment of international medical teams in West Africa, including from China and Cuba, may go some way to help.
Nigeria and Senegal, where the situation is judged "stable -- for the moment," are seen as success stories so far.
They have shown that conventional methods such as early detection, tracing of those who've been in contact with infected patients, isolation and adequate supply of personal protective equipment can contain the virus, WHO said.
"If Nigeria can control an outbreak caused by such a deadly and highly contagious virus, right from the start, any country in the world can do the same," its report said.