Camera zooms in and racks focus to microscopic view of Oriental rat flea (Xenopsylla cheopis). a well-known vector for bubonic plague. Plague is a deadly disease caused by the bacterium, Yersinia pestis. Humans usually get plague after being bitten by a rodent flea that is carrying the plague bacterium or by handling an animal infected with plague. This animation includes a dark, circular vignette meant to simulate the view through a microscope eyepiece.