Liberia, Guinea,  and Sierra Leone have been trying since March to stop what has become the largest Ebola outbreak ever recorded—as of August 6, 932 people have died from the disease and more than 1,700 people have been sickened. There have been cases in Nigeria and two Americans who came down with the disease while treating patients in West Africa are being treated in Atlanta. For this week’s Please Explain, W. Ian Lipkin, John Snow Professor of Epidemiology and director of the Center for Infection and Immunity at Columbia University’s Mailman School of Public Health, talks about the Ebola outbreak and how other infectious diseases outbreaks are contained and halted.