Capillaria philippinensis life cycle

Typically, unembryonated eggs are passed in the human stool (1) and become embryonated in the external environment (2); after ingestion by freshwater fish, larvae hatch, penetrate the intestine, and migrate to the tissues (3). Ingestion of raw or undercooked fish results in infection of the human host (4). The adults of Capillaria philippinensis (males: 2.3 to 3.2 mm; females: 2.5 to 4.3 mm) reside in the human small intestine, where they burrow in the mucosa (5). The females deposit unembryonated eggs. Some of these become embryonated in the intestine and release larvae that can cause autoinfection. This leads to hyperinfection (a massive number of adult worms) (6). C. philippinesis is currently considered a parasite of fish eating birds, which seem to be the natural definitive host (7).