Disease outbreaks are unpredictable and often deadly. Wherever they occur on the planet, we are all potentially at risk: in our era of globalized air travel, a microbe can make it round the world in less than 24 hours. Alongside outbreaks of well-established diseases such as influenza, yellow fever, plague, cholera and measles, we are also seeing many outbreaks caused by more "recent" pathogens identified since the 1970s, including HIV, SARS, hepatitis C, MERS-CoV and Ebola.