The Ebola outbreak has spawned a “silent killer,” experts say: hidden cases of malaria, pneumonia, typhoid and the like that are going untreated because people in the countries hardest hit by the dreaded virus either cannot find an open clinic or are too afraid to go to one. Evidence of what the World Health Organization calls an “emergency within the emergency” is everywhere in Guinea, Liberia and Sierra Leone, the West African countries worst hit by the Ebola epidemic.