The World Health Organization will send experts to test the Ebola-preparedness measures in Cote d'Ivoire and Mali, the two countries at greatest risk of being the next to be affected by the epidemic, WHO's health security response chief, Isabelle Nuttall, said on Thursday.

The virus is known to have killed almost 4,500 people in Liberia, Sierra Leone and Guinea this year, and there have been isolated cases in the United States, Germany and Spain.

The WHO says there have been 9,000 recorded cases in West Africa and a similar number unrecorded, with a 70 percent fatality rate, implying a true death toll already above 12,000. The WHO expects 5,000 to 10,000 new cases a week by December.