The correct answer is C, dog or cat fleas.  Fleas ingest Dipylidium caninum eggs.  These hatch in the fleas where they become cysticercoid larvae.  In most cases, infection occurs in children under 5 years old and infants under 6 months of age by accidental ingestion of the infected flea.

Click here to open a new window with a schematic diagram showing the life cycle of Dipylidium caninum.  Close the new window to return to this page.