Here, bubonic plague bacteria (yellow) are shown in the digestive system of a rat flea (purple). The bubonic plague killed a third of Europeans in the mid-14th century. Today, it is still active in Africa, Asia, and the Americas, with as many as 2,000 people infected worldwide each year. If caught early, bubonic plague can be treated with antibiotics.

This image was part of the Life: Magnified exhibit that ran from June 3, 2014, to January 21, 2015, at Dulles International Airport.