Imagine a world in which the AIDS virus, HIV, kills in two weeks not in ten years. Now imagine that HIV, like the flu, can be spread by the simple act of coughing or sneezing. Dispersed around the world at the speed of a passenger jet, such a virus could pose a threat to the entire human species. Now imagine that a virus which may have such a potential has already emerged. Because it has, in the form of Ebola.