American virologist Joseph Fair has been living in Sierra Leone for much of the last decade, most recently advising the ministry of health on how to cope with the Ebola outbreak. Last month, when he visited the community hospital in Kenema, 186 miles (300 km) inland from the capital city of Freetown, he greeted old friends with warm embraces. Within two weeks, three of them were dead, felled by Ebola, which the World Health Organization Friday declared a Public Health Emergency of International Concern, its highest level of alert.

With his grief still raw, Fair, a special advisor to the ministry of health, works 12-plus-hour days helping to coordinate the country's response to the largest Ebola outbreak in history. Fair