Bat fleas

In "Batman: Shadow of the Bat" #11, there is a story "The Human Flea", Batman visits Kemp's Flea Circus in Gotham City as a part of his investigations, the story concludes in edition #12.



"Mortimer Kadaver escapes from incarceration along with animal rights activist Jan Brodie. Meanwhile, Batman encounters the Human Flea, who has been committing robberies in order to fund his grandfather's unsuccessful flea circus. Kadaver arranges for Brodie and his collegues to raid a laboratory in order to make sure thatin his exit from this world, he takes as many people along with him as possible.

Kadaver plans to destroy Gotham by plague, stealing both fleas and a sample of the pleague baccilus. He is stopped by Batman and the Human Flea, whose grandfather he murdered to secure the fleas, and is prevented from committing suicide as well."

Ref: Unofficial History of the DC Universe

Batman: Shadow of the Bat #11 (April 1993): "The Flea, part 1"
Batman: Shadow of the Bat #12 (May 1993): "The Flea, part 2"