Description, Causes and Risk Factors

Metagonimiasis is an infectious parasitic disease that is associated with eating undercooked fish. It is found mostly in the far east, but also in Siberia, Manchuria, the Balkan states, Israel and Spain.

This disease is caused by an intestinal trematode, mostcommonly Metagonimus yokagawai, but sometimes by M. takashii or M. miyatai. Metagonimus yokagawai,also called the Japanese fluke. Much more rarely, metagonimiasis can arise from infection with M. takahashii or M. miyatia. Recent studies analyzing the DNA of the three agents causing Metagonimiasis found that DNA sequencing supports M. yokagawai and M. takahashii be placed in the same clade, and phylogenic tree analysis supports their genetic similarity M. miyatia.

Life cycle:

Embryonated eggs each with a fully-developed miracidium (the ciliated first-stage larva of a trematode that emerges from the egg and must penetrate into the tissues of an appropriate intermediate host snail if it is to continue its life cycle; followed by development into a mother sporocyst and by production of a number of offspring of successive larval generations) are passed in feces.

  • Snail hosts ingests eggs, miracidia emerge from eggs and penetrate the snails intestine.
  • Cercariae released from snail.
  • Cercarlae penetrate the skin of fresh/brackish water fish and encyst as metacercariae in the tissue of the fish.
  • Host become inefcted by ingesting undercooked fish containing metacercariae.
  • Metacercariae excyst in the small intestine.
  • Adult in small intestine.
  • Fish-eating mammals and birds can be infected as well.

Metagonimiasis is transmitted through eating undercooked fish caught in water polluted with infected fecal matter. By nature of its mode of transmission, M. yokogawai tends to be more a disease of rural and underprivileged populations. Because of this, public health measures that rely on mass screening and drug therapy of infected people are likely to encounter difficulties with funding and delivery.

The incubation period is around 14 days and infestation may persist for more than one year.


The symptoms are caused by an intestinal worm of the Trematode family. The scientists originally named the parasite Heterophyes yokogawai because of its great similarity to the intestinal trematode Heterophyes heterophyes. However, following further research by Yokogawa on human subjects and experimental dogs that showed the two parasites to be morphologically different, they later renamed the fluke Metagonimus yokogawai.

Signs and symptoms:

Peripheral eosinophilia.

  • Diarrhea.
  • Nausea.
  • Abdominal pain.
  • Lethargy.
  • Fatigue.
  • Anorexia.
  • Malaise.
  • Seizures (in extreme cases).
  • Neurological defects (in extreme cases).
  • Cardiac problems (in extreme cases).


The diagnosis is based on the microscopic identification of eggs in the stool. However, the eggs are indistinguishable from those of Heterophyes heterophyes and resemble those of Clonorchis and Opisthorchis. Specific diagnosis is based on identification of the adult fluke evacuated after antihelminthic therapy, or found at autopsy.


Treatment Options:

Praziquantel, Niclosamide, Bithionol.

Studies in rats and rabbits have shown the drug to increase abortion rates and to have teratogenic effects when given in doses that exceed the recommended human dose. In addition, Praziquantel is excreted in breast milk, and so should not be used while a mother is breastfeeding.

  • It is administered orally, and does not require heavy dosage. Its potential applications for mass therapy are promising.
  • Prophylactic treatment should also be coupled with therapy to address secondary clinical symptoms.
  • With heavy infections, hydration and electrolyte therapy should be administered to counter fluid and salt losses due to diarrhea.

Preventive Measures:

Establish hygienic sanitary waste disposal systems.

  • Encourage thorough cooking practices.
  • Do not eat undercooked fish.
  • Wash hands properly after handling raw fish.
  • Wash the utensils and knife after cutting raw fish.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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