In two Land Rovers, one fitted out as an ambulance, a small team of humanitarian workers last week headed deep into Sierra Leone's jungle. After hours on deeply rutted paths that could barely be called roads, they stopped at a village that had seen ten reported cases of Ebola.

With the consent of the village chief, the team fanned out across the community, asking at each hut if anyone was feeling ill or had made contact with the earlier patients. At one, they found a mother nursing a 7-month-old, even though she had experienced bouts of bloody diarrhea and a fever of 102°F—possible signs of Ebola. A quick conversation revealed that the mother had recently attended the same funeral as the