Plague or Black Death could re-emerge

[Northerner]

Scientists have discovered that two of the world's most devastating plagues -- the plague of Justinian and the Black Death, each responsible for killing as many as half the people in Europe -- were caused by distinct strains of the same pathogen, one that faded out on its own, the other leading to worldwide spread and re-emergence in the late 1800s. These findings suggest a new strain of plague could emerge again in humans in the future.

http://www.sciencedaily.com/releases/2014/01/140127193741.htm