As the past few years have painfully made clear, infectious diseases remain one of humanity’s greatest perils. It only took weeks for scientists to identify the cause of the covid-19 pandemic—a previously unknown species of coronavirus—but there have been plenty of outbreaks, past and present, whose true cause isn’t so obvious. Here are six mysterious outbreaks that remain unsolved.
A version of this story was originally published April 2, 2021.
