GENEVA — The number of people in West Africa who have contracted the Ebola virus and died from the hemorrhagic fever that it causes has doubled in the past month, the World Health Organization reported on Thursday.

In Guinea, Liberia and Sierra Leone, the three countries hardest hit by the Ebola outbreak, a total of 5,335 people have been infected and 2,622 have died, the organization reported. The tally a month ago was 2,458 infections and 1,346 deaths.