GENEVA, October 29. /TASS/. The number of Ebola cases has exceeded 13,700, the World Health Organisation's Assistant Director-General Dr. Bruce Aylward said on Wednesday.

The deadly virus has already killed more than 5,000 people, mainly in Guinea, Liberia and Sierra-Leone, he said.

Most Ebola cases (6,535) were reported in Liberia, Aylward said adding that the WHO was "cautiously optimistic" that the rate of new cases in this West African country was slowing down.

"We are seeing slowing rate of new cases, very definitely," he said.

Aylward also said that Ebola cases were also reported in Mali, Spain and the United States, while Nigeria and Senegal were declared Ebola-free.

Ebola virus outbreak 

The Ebola virus disease, previously known as the Ebola hemorrhagic fever, is a severe illness in humans, often fatal, according to the WHO. The virus is passed on to people from wild animals and can be transmitted from humans to humans. The average EVD case death rate is some 50%

The first outbreaks of the EVD occurred in remote Central African villages, near tropical rainforests. However, major urban and rural areas have been involved in the most recent outbreak in western Africa.

Early supportive care, which includes rehydration and symptomatic treatment, improves the survival rate. No licensed treatment has yet been proven to be able to neutralize the virus but a number of blood, immunological and drug medications are under development. There are no licensed Ebola vaccines yet but two candidates are being evaluated.