The UN health agency reported that as of December 10, there had been 18,188 cases of infection from the deadly virus in Guinea, Liberia and Sierra Leone, of whom 6,583 people had died.
WHO did not provide an update of cases in other countries, but on Wednesday said the death toll remained the same: six in Mali, one in the United States, and eight in Nigeria, which was declared Ebola free in October.
Spain and Senegal, which have both been declared free from Ebola, meanwhile counted one case each, but no deaths.
Sierra Leone, which earlier this week overtook Liberia as the nation with the most infections, counted 8,069 cases and 1,899 deaths on December 10.
The toll up until December 7 stood at 7,897 cases and 1,768 deaths.
Liberia, long the hardest-hit country, has meanwhile seen a clear decrease in transmission over the past month.
As of December 7, the country counted 7,765 cases and 3,222 deaths, up from the 7,719 infections and 3,177 deaths tallied four days earlier.
In Guinea, where the outbreak started nearly a year ago, 2,354 Ebola cases and 1,462 deaths were recorded as of December 10. Three days earlier, the country counted 2,292 Ebola cases and 1,428 deaths.
Ebola, one of the deadliest viruses known to man, is spread only through direct contact with the bodily fluids of an infected person showing symptoms such as fever or vomiting.
People caring for the sick or handling the bodies of people infected Ebola are especially exposed.
As of December 7, a total of 639 healthcare workers were known to have contracted the virus, and 349 of them had died, WHO said.