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Metagonimiasis

[Metagonimus yokogawai]

Adult M. yokogawai, stained with carmine.  In this figure, the following structures are labeled:  oral sucker (OS), pharynx (PH), intestine (IN), genitoacetabulum (GA), ovary (OV), the large, paired testes (TE), and eggs within the uterus (EG).

Adult M. yokogawai, stained with carmine. In this figure, the following structures are labeled: oral sucker (OS), pharynx (PH), intestine (IN), genitoacetabulum (GA), ovary (OV), the large, paired testes (TE), and eggs within the uterus (EG).


Snails in the genus, Semisulcospira. Images courtesy of Conchology, Inc, Mactan Island, Philippines.

Snail in the genus, Semisulcospira. Images courtesy of Conchology, Inc, Mactan Island, Philippines.

Causal Agents

Metagonimus yokogawai, a minute intestinal fluke (and the smallest human fluke).


Life Cycle

Life cycle of Metagonimiasis Life Cycle:

Adults release fully embryonated eggs each with a fully-developed miracidium, and eggs are passed in the host’s feces The number 1. After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia which penetrate the snail’s intestine The number 2. Snails of the genus Semisulcospira are the most frequent intermediate host for Metagonimus yokogawai. The miracidia undergo several developmental stages in the snail, i.e. sporocysts The number 2a, rediae The number 2b, and cercariae The number 2c. Many cercariae are produced from each redia. The cercariae are released from the snail The number 3 and encyst as metacercariae in the tissues of a suitable fresh/brackish water fish (second intermediate host) The number 4. The definitive host becomes infected by ingesting undercooked or salted fish containing metacercariae The number 5. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestine The number 6 and mature into adults (measuring 1.0 mm to 2.5 mm by 0.4 mm to 0.75 mm) The number 7. In addition to humans, fish-eating mammals (e.g., cats and dogs) and birds can also be infected by M. yokogawai The number 8.

Geographic Distribution

Mostly the Far East, as well as Siberia, Manchuria, the Balkan states, Israel, and Spain.

Clinical Presentation

The main symptoms are diarrhea and colicky abdominal pain. Migration of the eggs to extraintestinal sites (heart, brain) can occur, with resulting symptoms.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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