Intestinal Flukes Clinical Presentation

Updated: Feb 21, 2019
  • 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.

In severe infection, diarrhea may alternate with constipation. Hunger pangs may be one of the first symptoms to appear, usually occurring near the end of the incubation period. Minimal bleeding at the site of attachment may manifest as bloody diarrhea. As the infection progresses and the worm burden increases, intoxication results from the absorption of worm metabolites by the host. [38] The patient then experiences toxic and allergic symptoms such as edema of the face, abdominal wall, and lower limbs. Patients may report increased abdominal girth and abdominal pain. Anorexia, nausea, and vomiting are also common. The diarrhea persists, becoming greenish-yellow and exceptionally malodorous.

Heavy F buski infection may cause intestinal obstruction. On the other hand, eggs of H heterophyes may embolize, causing myocarditis, heart failure, and intracerebral hemorrhage. Eggs lodged in the spinal cord may manifest as motor and sensory deficits at the level of the lesion. [38]

Mild to moderate infections with the liver flukes C sinensis and O viverrini may also manifest as symptoms similar to those of intestinal flukes. However, distinction between these parasites is important, as these liver flukes are known to be associated with the development of cholangiocarcinoma. [39]



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 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.