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)



Geographic Distribution


Freshwater plants (water caltrop, water chestnut)

China, Thailand, Bangladesh, India


Tadpoles, freshwater snails, fish, frogs

Indonesia, Philippines, Taiwan, Thailand



Egypt, Iran, Tunisia, Turkey


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)



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


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


Fever, abdominal pain, anorexia, weight loss, diarrhea, pancreatitis

Carneophallus brevicaeca


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.