More than 20,000 people have been infected by the deadly Ebola virus in the three worst-affected West African countries as the death toll nears 8,000.

More than 20,000 people have been infected by the deadly Ebola virus in the three worst-affected West African countries as the death toll nears 8,000, the World Health Organization has announced in its latest update on the disease.

The UN health agency said in statement on Monday that the Ebola outbreak had killed more than 7,842 people and 20,081 cases had been reported in Sierra Leone, Liberia and Guinea.

Sierra Leone had the highest number of Ebola cases of the three intense-transmission countries, with 9,409 cases having been reported to date.

Liberia's death toll of 3,413 was more than the 2,732 recorded in Sierra Leone.

In Guinea, 1,697 deaths have been reported out of 2,695 cases.