Michael Crichton’s 1969 novel The Andromeda Strain tells of a space-based organism that is brought back to earth by a crashed satellite. The mysterious crystalline life form instantaneously kills almost every person it comes into contact with. The Andromeda Strain is a work of fiction, but many have wondered if a similar scenario could happen in real life—whether an undiscovered or newly mutated virus or other organism (not necessarily from space) could create a worldwide epidemic or even human extinction. Indeed, the term “Andromeda strain” itself has come into common usage to describe such an entity.

Some people consider the Ebola virus a potential real-life Andromeda strain. First discovered in Africa in 1976, its origins remain a mystery. The virus, for which there is no cure or vaccine, kills people gruesomely by clotting their...