Life Cycle of Trypanosma brucei gambiense and Trypanosma brucei rhodesiense  
     
  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  .