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Intestinal flukes (Fasciolopsis, Heterophyes, Metagonimus, Echinostoma)

  • Parasite
  • For completeness

Flatworms that live in the small intestine after eating raw water plants, fish or snails. Mostly Asian; usually mild, heavy loads cause diarrhoea.

Updated

Also called: Fasciolopsis buski, giant intestinal fluke, Heterophyes heterophyes, Metagonimus yokogawai, Echinostoma spp.

Quick facts

Type
Parasite · Trematodes (flukes)
Gram / shape
Leaf-shaped flukes
Spread
Fasciolopsis · Heterophyes and Metagonimus
Causes
Fasciolopsiasis · Heterophyiasis and metagonimiasis
Treatment
Praziquantel is the drug of choice for intestinal flukes

At a glance

Shape
Leaf-shaped flukes; operculated eggs
Family
Fasciolidae (Fasciolopsis); Heterophyidae (Heterophyes, Metagonimus); Echinostomatidae (Echinostoma)
Type
Food-borne digenean trematodes of the small intestine
Size
Fasciolopsis up to several centimetres (the largest human intestinal fluke); heterophyids 1–2.5 mm (the smallest)

Morphology

  • Fasciolopsis egg: large, operculated, 130–150 µm, almost identical to the Fasciola hepatica egg.
  • Heterophyes and Metagonimus eggs: tiny, embryonated, resembling Clonorchis and Opisthorchis eggs.
  • Echinostoma: a collar of spines around the oral sucker; large eggs that resemble Fasciola eggs.
  • Eggs alone often cannot name the genus; the adult fluke is needed.

Transmission

  • Fasciolopsis: eating raw water plants (water chestnut, water caltrop) with metacercariae.
  • Heterophyes and Metagonimus: eating raw, undercooked or salted freshwater or brackish fish.
  • Echinostoma: eating raw snails, clams, fish or tadpoles.

Reservoir: Fasciolopsis: pigs and humans; Heterophyids: fish-eating mammals and birds; Echinostoma: birds and mammals; snails and other aquatic animals as intermediate hosts

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. Eggs leave in the stool and reach fresh water.
  2. A miracidium (or the egg itself, in heterophyids) infects a specific snail.
  3. In the snail the fluke multiplies through sporocyst and redia stages and releases cercariae.
  4. Cercariae encyst as metacercariae on water plants (Fasciolopsis) or in fish, snails or tadpoles.
  5. A person eats the raw plant or animal; metacercariae excyst and adults attach to the small intestine.

Virulence factors

  • Attachment of the flukes causes local inflammation and ulcers of the mucosa.
  • Heavy Fasciolopsis loads cause malabsorption, oedema and ascites (protein loss) or obstruction.
  • Heterophyid eggs can enter the circulation and lodge in the heart or brain.

Diseases it causes

  • Fasciolopsiasis: diarrhoea, abdominal pain, oedema and ascites in heavy infections
  • Heterophyiasis and metagonimiasis: diarrhoea and colicky pain; rarely egg emboli to the heart or brain
  • Echinostomiasis: abdominal pain, diarrhoea and eosinophilia

Clinical picture

  • Most infections are light and asymptomatic.
  • Heavy infections: diarrhoea, epigastric pain, anorexia, weight loss.
  • Fasciolopsis: facial and generalised oedema, ascites, intestinal obstruction.
  • Eosinophilia is common.

Diagnosis

  • Eggs in stool (or vomitus for Fasciolopsis) on direct smear or concentration.
  • Measure eggs: large ones point to Fasciolopsis, Fasciola or Echinostoma; tiny ones to heterophyids or Clonorchis.
  • Species identification needs adult flukes passed after treatment.

Treatment

Praziquantel is the drug of choice for intestinal flukes; triclabendazole, used for Fasciola, is not the standard for these.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Cook water plants, fish, snails and clams; peel or dip water plants in boiling water.
  • Do not use untreated human or pig faeces to fertilise fish ponds or water crops.
  • Sanitation; a One Health approach combining food safety and veterinary measures.

Test yourself

Think of the answer, then tap the question to see it.

Which is the largest intestinal fluke of humans and how is it acquired?

Fasciolopsis buski, by eating raw water plants carrying metacercariae.

Which liver fluke egg is almost identical to the Fasciolopsis egg?

The Fasciola hepatica egg.

Which food transmits Heterophyes and Metagonimus?

Raw, undercooked or salted freshwater or brackish fish.

What drug is used to treat intestinal fluke infections?

Praziquantel.

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Connections

← Back to the group: Trematodes (flukes)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: CDC - DPDx - Fasciolopsiasis (CDC, 2024); CDC - DPDx - Heterophyiasis (CDC, 2018); CDC - DPDx - Metagonimiasis (CDC, 2017); CDC - DPDx - Echinostomiasis (CDC, 2019).

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Representative model, for educational purposes only.