Healthy rats contracted plague from infected rats when the only apparent means of communication between the two was the rat flea (pulex cheopis).
The related species of the Oestridae family, which include the widely disseminated chigoe or bicho do pe (Pulex penetrans), and the equally troublesome berne (Cutiterebra noxialis), which is so injurious to animals, are equally numerous.
This is by far the largest family and contains the commonest species; the larva of Echinorhynchus proteus lives in Gammarus pulex and in small fish, the adult is common in many fresh-water fish: E.
Fleah, or flea, cognate with flee, to run away from, to take flight), a name typically applied to Pulex irritans, a well-known blood-sucking insect-parasite of man and other mammals, remarkable for its powers of leaping, and nearly cosmopolitan.
At least four species of fleas (including Pulex irritans) which infest the common rat are known to bite man, and are believed to be the active agents in the transmission of plague from rats to human beings.