GENEVA (AP) — The Ebola outbreak in West Africa is accelerating and could grow six times larger to infect as many as 20,000 people, the World Health Organization said Thursday. The U.N. health agency unveiled a new road map for containing the virus, and scientists are fast-tracking efforts to find a treatment or vaccine.

Ebola has menaced Africa for 40 years, but previously struck in remote villages and was contained fairly quickly. This time, it has spread to major cities in four countries, provoking unrest as whole neighborhoods and towns have been sealed to the outside.