The virus has spread rapidly over the past 21 days, and the number of patients increased significantly.
The WHO added that the disease continued to expand through Guinea, Liberia and Sierra Leone. Its incubation period is 21 days, which is why the WHO conducts a new analysis every three weeks.
Until Sep 6, Guinea had recorded 862 infections and 555 deaths. But over the 21-day period just concluded, there were an additional 339 infections and 155 deaths reported.
In Liberia, 2,064 infections were recorded, of which 1,224 resulted in the deaths of those stricken by the virus. The increase over the same time-frame added 1,212 infections and 758 deaths to the mounting toll.
WHO: Ebola virus has spread rapidly over the past 21 days
The WHO said that it expected thousands of new infections during the upcoming three weeks in Liberia, where there is one doctor for every 100,000 people in a country with a population of 4.4 million.
In Sierra Leone, 1,361 people were infected and 509 died, with an increase of 533 infections and 154 deaths.
Of the 4,269 cases recorded to date in those three countries, 2,048 of the infections occurred in the past three weeks. Of the total number of 2,228 deaths, 1,067 occurred during the same period.
In Nigeria, eight infections and four deaths were recorded in the past 21 days. The total toll there is 21 infections and eight deaths.
Three infections -- none of these happened in the past three weeks -- and no deaths were reported in Senegal.
This is the biggest outbreak of the deadly Ebola virus disease since the virus was discovered in the Democratic Republic of Congo (then called Zaire), in 1976. There is no known cure for the infection, which has a high mortality rate.