Causal Agent:
The trematode Heterophyes heterophyes, a minute intestinal fluke.

Life Cycle:

Adults release embryonated eggs each with a fully-developed miracidium, and eggs are passed in the host's feces .  After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia which penetrate the snail’s intestine .  Genera Cerithidia and Pironella are important snail hosts in Asia and the Middle East respectively.  The miracidia undergo several developmental stages in the snail, i.e., sporocysts , rediae , and cercariae .  Many cercariae are produced from each redia.  The cercariae are released from the snail and encyst as metacercariae in the tissues of a suitable fresh/brackish water fish (second intermediate host) .  The definitive host becomes infected by ingesting undercooked or salted fish containing metacercariae .  After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine and mature into adults (measuring 1.0 to 1.7 mm by 0.3 to 0.4 mm) .  In addition to humans, various fish-eating mammals (e.g., cats and dogs) and birds can be infected by Heterophyes heterophyes .

Geographic Distribution:
Egypt, the Middle East, and Far East.