More than 1,000 people have died, with Sierra Leona, Guinea and Liberia worst-affected and two deaths in Nigeria, Africa's most populous country.

The World Health Organization (WHO) has declared an International Public Health Emergency.

Ebola outbreak

Researchers from the New England Journal of Medicine have traced the outbreak to a two-year-old girl, who died on 6 December 2013 in a small village in south-eastern Guinea.

Cumulative death toll

The WHO has published updates on the spread of the virus in each of the countries affected.

The World Health Organization has declared the Ebola outbreak in West Africa to be an international public health emergency that requires an extraordinary response to stop its spread.

It is the largest and longest outbreak ever recorded of Ebola, which has a death rate of about 50 per cent and has so far killed at least 932 people.

"Countries affected to date simply do not have the capacity to manage an outbreak of this size and complexity on their own," WHO chief, Dr. Margaret Chan, said at a news conference in Geneva. "I urge the international community to provide this support on the most urgent basis possible."

In the United States, the Centers for Disease Control and Prevention have already elevated their Ebola response to the highest level and have recommended against travelling to West Africa. On Thursday, CDC director Dr. Tom Frieden told a Congressional hearing that the current outbreak is set to sicken more people than all previous outbreaks of the disease combined.

The World Health Organization is launching a $100 million response plan to combat an "unprecedented" outbreak of Ebola in West Africa that has killed 729 people out of 1,323 infected since February.