DAVOS: United Nations agencies need a final $1 billion to fight West Africa’s deadly Ebola epidemic as experts move to a new phase involving a massive detective operation to trace remaining cases, the UN Ebola chief said on Wednesday.

David Nabarro estimated that an overall total of $4 billion in new money, equivalent to all the aid committed so far, was needed by relief agencies and the worst affected countries themselves to end the epidemic and “help these countries to get back to the economic trajectory they had.”

The unprecedented outbreak has so far killed more than 8,400 people, overwhelmingly in Liberia, Guinea and Sierra Leone, and the international response has included balance of payments and military support as well as medical help.

So far, UN bodies have received around $1 billion, two-thirds of a target set last year. Nabarro, who heads the UN response, said at the World Economic Forum in Davos that the World Health Organization, UNICEF and the World Food Programme now needed the same amount again.