New figures showed the massive scale of the crisis, which the WHO said indicated a ‘rapid increase still in the intensity of transmission’ that could cost at least USD 490 million (370 million euros) to tackle.
Bruce Aylward, the WHO's head of emergency programmes said that it could take six to nine months to bring Ebola under control, by which time the number of infections could have passed 20,000.
"That's not saying we expect 20,000, that's not saying we would accept, more importantly, 20,000 cases," he told reporters in Geneva, calling the situation a "global health security issue".
"But we have got to have a system that is robust enough to deal with a very bad case scenario."
As of August 26, 1,552 people had been confirmed dead from Ebola in four countries, Sierra Leone, Liberia, Guinea and Nigeria while 3,062 had been infected.

Ebola claims over 1, 500 lives since February
Over 3,062 people reported infected
Ebola cases may exceed 20,000
It needs USD 490 million for tackling Ebola
WHO calls Ebola situation global health security issue
Health ministers of ECOWAS vowed to strengthen their responses to devastating outbreak

Liberia was the worst affected with 694 deaths; 422 people have died in Sierra Leone; and 430 in Guinea, where the virus emerged at the start of the year. Nigeria has now recorded six deaths.
But Aylward warned that the actual caseload could be "two to four times higher than the number of cases you see reported".
Nigeria's latest death in the southeastern oil city of Port Harcourt was the first outside its biggest city, Lagos, and dashed hopes that the country had successfully contained the virus.
Scientists meanwhile said the first human trials of a potential vaccine will start next week using a product known as the NIAID/GSK Ebola vaccine candidate made by pharmaceuticals giant GlaxoSmithKline and US government.
Health ministers from member states of the West African regional bloc ECOWAS met today in the Ghanaian capital Accra and vowed to strengthen their response to the devastating outbreak.
Ghana's President John Mahama, the current ECOWAS chairman, complained security measures taken by other countries to prevent the virus spreading, including travel bans, had unfairly hit member states.
"Currently in the sub-region, Ebola is officially reported in four countries and yet the entire West African sub-region of 15 nations and even Africa as a whole of 54 nations has been stigmatized," he said.


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