The UN health agency said a total of 4,985 people had been infected across five west African countries, and that 2,461 had died.
In the three hardest-hit countries of Guinea, Libera and Sierra Leone, nearly half of the cases were recorded in the past three weeks, WHO said.
In Guinea, where the outbreak began at the start of the year, Ebola had as of September 13 claimed 595 lives, or 64 per cent of the 936 people infected.
Thirty-three per cent of those cases surfaced in the 21 days leading up to September 13.
In Liberia, which has been hardest-hit by the outbreak, 1,296 people had died from Ebola as of September 9, representing 54 per cent of the 2,407 people infected.
A full 57 per cent, or 1,383, of those cases were recorded during the three weeks before September 9.
In Sierra Leone, 562 people had died from Ebola by September 13, accounting for 35 per cent of the 1,620 people infected.
Forty per cent of those cases were recorded during the preceding 21 days.
Nigeria had meanwhile, as of September 13, seen eight Ebola deaths since the virus first arrived in the country with a Liberian finance ministry official who died in Lagos on July 25.
That amounts to 38 per cent of the 21 cases. Six of those cases have emerged in the past three weeks.
Senegal’s only confirmed Ebola case a Guinean student who crossed the border just before it was closed on August 21 has recovered, but the country will not be declared transmission free before 42 days have passed since the case was recorded.