Plague. The word itself is like a blow, connoting misery, miasma and death. Plague takes many forms: influenza, typhus, cholera, the Black Death, and, recently, AIDS. AIDS has reminded us that epidemic infectious disease is not simply a historical phenomenon--or one limited like famine to remote continents --and is a vivid and painful illustration of how epidemics take place at a number of levels --biological event, social perception, collective...