An experimental serum treatment on two US missionaries has raised hopes of an effective treatment for the disease after doctors reported a "miraculous" improvement in the health of one of those who contracted the disease.
The development came as a leading British scientist claimed the end of the Ebola epidemic may be in sight, with the disease already peaking in the county where the outbreak originated.
Chris Witty, an adviser to the Department for International Development and a professor of public and international health, said Guinea had already seen the worst of the outbreak and cases were now beginning to decrease.
• US preparing to receive Ebola patient
Although the number of infections is continuing to rise in Sierra Leone and Liberia, Prof Witty said the situation was likely to peak soon and then the epidemic would begin to decline.
"The outbreak is very unusual," he said in a podcast. "This is the largest outbreak of Ebola that so far has been recorded. The numbers are increasing in Sierra Leone but they appear to have peaked in Guinea where the epidemic first started.
"What we hope is that with good management and good control we should be able to start to see the peak of the epidemic and then it will start to decrease."
As the death toll from the epidemic in west Africa reached at least 887 by August 1, the total number of cases in the four west African countries affected stood at 1,603 on the same date, the World Health Organisation said.
The body also confirmed that Nigeria was now dealing with four cases of Ebola, including a doctor who treated Patrick Sawyer, a US lawyer who died in Lagos last month after contracting the disease in Liberia, spreading panic in Africa's biggest city. Just three vials of the experimental serum known as "ZMapp", which had only previously been tested on monkeys, were flown to Liberia for the treatment of two US missionaries.
Dr Kent Brantly, 33, who has since been flown to an isolation unit in Atlanta, at first insisted that the serum be given to his older colleague, Nancy Writebol, 59, but when his own condition deteriorated sharply he was given the first dose.
"Within an hour of receiving the medication, Brantly's condition was nearly reversed. His breathing improved; the rash over his trunk faded away. One of his doctors described the events as 'miraculous'," reported CNN, citing sources with first-hand knowledge of the situation.
A flight carrying Ms Writebol, who is in a "serious" condition, has left Liberia headed for Atlanta.
"ZMapp", which had been developed by a San Diego-based company, Mapp Biopharmaceutical, is one of a class of new drugs known as "monoclonal antibodies" that use proteins to prevent the Ebola virus from infecting new cells.
The threat of the Ebola outbreak cast a shadow over an US-Africa Summit that opened in Washington DC yesterday attended by nearly 50 African heads of state, although the presidents of Liberia and Sierra Leone were forced to cancel.
The summit was meant to present Africa as an investment destination and break stereotypes about the Continent as a place of war and disease.