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[Philophthalmus spp.]

Fully-embryonated eggs are shed into the water from the definitive host’s eyes .  Miracidia hatch almost immediately in water and penetrate the snail intermediate host . Several snail genera may serve as intermediate hosts, including Thiara spp. and Melanoides spp.  Inside the snail host, the miracidia (which contain a pre-formed redia) undergo a series of stages (, ) and become cercariae.  Cercariae are released from the snail and encyst on aquatic vegetation or other solid objects in the water .  The definitive host, which is usually an aquatic bird, becomes infected upon ingestion of metacercariae .  Metacercariae excyst in the mouth and migrate to the eye where the adults reside .  Humans rarely serve as incidental hosts, but may do so when they ingest metacercariae on aquatic vegetation .