What is the risk to people from newly emergent viruses such as Ebola, MERS, or Zika? Why do scientists and public health officials become so concerned about outbreaks of new versions of familiar viruses such as flu strains H5N1 or H1N1? What is a pandemic and what causes one to occur? How do new infectious diseases arise? Why are some infectious diseases, that have been eliminated or brought under control, still regarded as threats to human health? What are the characteristics of certain viruses and bacteria that cause them to be considered bioterrorism risks? 

This special section provides a general overview of what emerging infectious diseases are, how they arise, and why they are of concern. It further describes specific infectious agents, discusses why each is considered a problem, and presents research that is being conducted within the department on agents that cause emerging infectious diseases, or that could potentially be used for bioterrorism.