Intestinal Flukes Clinical Presentation

Updated: Jul 14, 2016
  • Author: Joseph Adrian L Buensalido, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Humans become infected with intestinal flukes by consuming contaminated food and water that consists of or contains the second intermediate hosts (eg, vegetation, snails, fish).

Most infected persons are asymptomatic and exhibit no physical signs.

Individuals with moderate infection present with occasional loose stools, some weight loss, malaise, and, occasionally, generalized abdominal pain.

Severe infection, in which toxic diarrhea alternating with constipation and hunger pangs are the first symptoms to appear, usually occurs near the end of the incubation period. As the infection progresses and the worm burden increases, edema of the face, abdominal wall, and lower limbs occurs, as well as ascites and generalized abdominal pain. Anorexia, nausea, and vomiting are also common. The diarrhea persists, becoming greenish-yellow and exceptionally malodorous.

In persons infected with H heterophyes, embolization of the eggs can lead to myocarditis, chronic heart failure, and/or cerebral emboli.

C sinensis and O viverrini are known to be associated with the development of cholangiocarcinoma, so patients presenting with the latter may need to prompt investigation for the parasites. [31]



In mild infections, patients are asymptomatic on physical examination.

In severe infections, patients are asthenic, with gray and harsh skin and edema of the face and lower extremities.



Intestinal flukes are endemic in areas that contain abundant snail hosts (eg, China, Vietnam, India, other parts of Asia).

Table 1. Common Intestinal Trematode Infections* (Open Table in a new window)

Infection Source Geographic Distribution
Fasciolopsiasis Freshwater plants (water caltrop, water chestnut) China, Thailand, Bangladesh, India
Echinostomiasis Tadpoles, freshwater snails, fish, frogs Indonesia, Philippines, Taiwan, Thailand
Heterophyiasis Fish Egypt, Iran, Tunisia, Turkey
Metagonimiasis Fish (cyprinid) Far East, Spain, Eastern Europe
*Adapted with permission from Tribble D, Wagner KF. Trematode infections. Infectious Disease Practice. 1996;20:69-73.

Table 2. Commonly Associated Exposures and Clinical Features of Certain Intestinal Trematodes* (Open Table in a new window)

Infection Source Clinical Features
Alaria americana Undercooked frog legs Disseminated fatal thoracic, gastrointestinal, retroperitoneal, and CNS manifestations; intraocular infections
Echinostomiasis (16 species) Freshwater fish, aquatic plants, clams, snails, mollusks, contact with aquatic birds May be asymptomatic; mild abdominal pain, bloating, dyspepsia, diarrhea, eosinophilia
Fibricola species Tadpoles Abdominal pain, diarrhea, fever, eosinophilia
Fasciolopsis species Water chestnut, water calthrop, water bamboo, water morning glory lotus and water hyacinth May be symptomatic; may be subclinical; gastritis, nausea, diarrhea, eosinophilia; generalized edema in persons with heavy infection burden
Gastrodiscoides species Vegetables, aquatic plants Often asymptomatic; may manifest as abdominal pain and diarrhea in severe cases
Watsonius watsoni Water bamboo Severe diarrhea
Fischoederius elongates Aquatic plants Epigastric pain and vomiting
Heterophyes species Mullets, fish; brackish water May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss
Gymnophalloides seoi Oysters Fever, abdominal pain, anorexia, weight loss, diarrhea, pancreatitis
Carneophallus brevicaeca Shrimp Fatal when infection involves CNS and heart
Brachylaima ruminae Poultry, rats Abdominal pain, diarrhea
Metagonimiasis species Fish (ayu, golden carp) May be asymptomatic; intestinal mucosal disease, ulcer-related abdominal pain, dyspepsia, nausea, vomiting, diarrhea, weight loss
Nanophyetus salmincola Undercooked fish (eg, salmon, trout, steelhead) May be symptomatic; mild diarrhea, abdominal pain
*Adapted from Berger SA, Marr JS. Human Parasitic Diseases Sourcebook. 1st ed. Sudbury, MA: Jones and Bartlett; 2006.