A total of 127 suspected or confirmed cases of the disease have been reported. The number includes 14 health care workers, eight of whom have died.
There are also one confirmed case and eight suspected cases of Ebola in neighboring Liberia.
The highly infectious, viral disease is spread mainly through contact with bodily fluids. Health experts are warning people in the affected areas to thoroughly wash their hands and avoid contact with Ebola victims.
The WHO said in the sole confirmed case in Liberia, the victim has been put in isolation, and the people with whom she had contact are under medical observation.
The outbreak began in Guinea in February, and was notable because cases hundreds of miles apart were reported. The first cases in Conakry, the nation’s capital, were confirmed last week.
Neighboring Senegal has closed its border with Guinea, and Friday an airplane that departed from Conakry was briefly quarantined at a Paris airport.