CONAKRY, Guinea (AP) — A U.S. official touring the West African countries worst hit by the deadly Ebola virus expressed optimism Wednesday that the right strategies to fight the disease are in place, even as warnings mount over the deteriorating situation.

The World Health Organization warned that new cases are appearing at a rapid rate in Liberia, Guinea and Sierra Leone, though Nigeria and Senegal, which saw just a handful of cases are on the verge of being declared Ebola free.