The leader of infectious disease research in the U.S. government says that the pandemic of Zika virus spreading across the global south, which may be causing an epidemic of birth defects in South America, heralds a new kind of infectious disease threat. It is exploding at the same time and in the same areas as other diseases carried by the same vector, mosquitoes—and thus demonstrates that it is no longer enough to be prepared to counter one disease at a time.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, writes in a study released Wednesday in the New England Journal of Medicinewrites in a study released Wednesday in the New England Journal