More than 5,000 people have been confirmed to have contracted the virus in Sierra Leone and Guinea, according to the latest figures released by the World Health Organization (WHO).
That compares with a total of 2,300 confirmed cases and 2,500 deaths, according the agency.
“The current outbreak of the Ebola virus has been highly volatile and complex, and is not easily pinned down to a single country or region,” the WHO said in a statement.
“As the outbreak has continued to expand, it is becoming increasingly difficult to say precisely where the outbreak originates.”
The virus is transmitted by contact with bodily fluids and body secretions, such as sweat, vomit and feces.
It is also spread through direct contact with infected patients, who are known to have higher infection rates than those in the general population.
The WHO has called for the international community to focus on the health needs of patients who have come into contact with Ebola patients.