THE IDEA THAT HUMAN travel and migration play a crucial role in spreading infectious diseases has, finally and permanently, set up shop in our modern consciousness. Numerous books—The Coming Plague, Secret Agents: the Menace of Emerging Infectious Disease, The Hot Zone, and even Hollywood movies(Outbreak, based on the latter volume)—have driven home the message that we are all, like Pigpen with his cloud of dust, trailing behind us a miasma of bacteria and viruses.