Emerging viral diseases are a major challenge to the safety of the world in the 21st century. The emergence of Ebola virus, avian influenza H5N1, Nipah and Hendra viruses, severe acute respiratory syndrome coronavirus (SARS-CoV) and, more recently, the novel Middle East respiratory syndrome (MERS) CoV, and avian influenza H7N9 has revealed the need for a more comprehensive understanding of the drivers of infectious disease outbreaks.