Ebola is a deadly contagious disease. From 1975 to 2013, it killed about 1,500 people. But a 2014 epidemic killed more than six times that number. At first the outbreak was contained to one country. But soon it spread to two others--the virus was on the move, and people were scared. When two American healthcare workers became infected and were sent to the United States for treatment, many people feared a pandemic--an outbreak that would spread...