The Ebola outbreak in West Africa could eventually infect more than 20,000 people - more than six times as many as doctors currently know about - the World Health Organization (WHO) said Thursday as it called for a global response to the spread of the virus. The U.N.’s health agency warned that it needed $490 million to combat Ebola over the next six months as it set out a "roadmap" for tackling the outbreak. The death toll has climbed to 1, 552 and "continues to accelerate,” the agency said.

It came as a doctor in Nigeria's oil industry hub of Port Harcourt became the latest victim. The medic was infected by a man linked to the first case in Africa's most populous country, health ministry spokesman Dan Nwomeh said. Port Harcourt is a hub for expatriate workers in major international oil companies.

The U.S. government and drugmaker GlaxoSmithKline will announce Thursday that they are starting the first human trials of a vaccine against the deadly virus.

IN-DEPTH

- Alastair Jamieson