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Echinostomiasis

[Echinostoma spp.]

Egg of Echinostoma sp. in an unstained wet mount of stool.  Image taken at 400x magnification.

Egg of Echinostoma sp. in an unstained wet mount of stool. Image taken at 400x magnification.


Adult Echinostoma removed during a colonoscopy, stained with hematoxylin and eosin (H&E).

Adult Echinostoma removed during a colonoscopy, stained with hematoxylin and eosin (H&E).

Causal Agents

Trematodes in the genus, Echinostoma. The genus is worldwide, and about ten species have been recorded in humans, including E. hortense, E. macrorchis, E. revolutum, E. ilocanum and E. perfoliatum. .


Life Cycle

Life cycle of Echinostomiasis

Many animals may serve as definitive hosts for various echinostome species, including aquatic birds, carnivores, rodents and humans. Unembryonated eggs are passed in feces The number 1 and develop in the waterThe number 2. The miracidium takes on average 10 days to mature before hatchingThe number 3 and penetrating the first intermediate host, a snailThe number 4. Several genera of snails may serve as the first intermediate host. The intramolluscan stages include a sporocystThe number 4a, one or two generations of rediaeThe number 4b, and cercariaeThe number 4c. The cercariae may encyst as metacercariae within the same first intermediate host or leave the host and penetrate a new second intermediate hostThe number 5. Depending on the species, several animals may serve as the second intermediate host, including other snails, bivalves, fish, and tadpoles. The definitive host becomes infected after eating infected second intermediate hosts The number 6. Metacercariae excyst in the duodenumThe number 7 and adults reside in the small intestineThe number 8 .

Geographic Distribution

Worldwide, but human cases are seen most-frequently in southeast Asia and in areas where undercooked or raw freshwater snails, clams and fish are eaten.

Clinical Presentation

Catarrhal inflammation often occurs due to the penetration of the sharp-spined collar into the intestinal mucosa. In heavy infections, nausea, vomiting, diarrhea, fever and abdominal pain may occur.

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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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