GENEVA — The number of people falling victim to the Ebola virus in West Africa has dropped to the lowest level in months, the World Health Organization said on Friday, but dwindling funds and a looming rainy season threaten to hamper efforts to control the disease.

More than 8,668 people have died in the Ebola epidemic in West Africa, which first surfaced in Guinea more than a year ago. But the three worst-affected countries — Guinea, Liberia and Sierra Leone — have now recorded falling numbers of new cases for four successive weeks, Dr. Bruce Aylward, the health organization’s assistant director general, told reporters in Geneva.

Liberia, which was struggling with more than 300 new cases a week in August and September, recorded only eight new cases in the week to Jan. 18, the organization reported. In Sierra Leone, where the infection rate is now highest, there were 118 new cases reported in that week, compared with 184 in the previous week and 248 in the week before that.