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Fasciolopsiasis

[Fasciolopsis buski]

Causal Agents

The trematode Fasciolopsis buski, the largest intestinal fluke of humans.


Life Cycle

lifeCycle

Immature eggs are discharged into the intestine and stoolThe number 1. Eggs become embryonated in water The number 2, eggs release miracidia The number 3, which invade a suitable snail intermediate host The number 4. In the snail the parasites undergo several developmental stages (sporocysts The number 4a, rediaeThe number 4b, and cercariae The number 4c ). The cercariae are released from the snail The number 5 and encyst as metacercariae on aquatic plants The number 6. The mammalian hosts become infected by ingesting metacercariae on the aquatic plants. After ingestion, the metacercariae excyst in the duodenum The number 7 and attach to the intestinal wall. There they develop into adult flukes (20 to 75 mm by 8 to 20 mm) in approximately 3 months, attached to the intestinal wall of the mammalian hosts (humans and pigs) The number 8. The adults have a life span of about one year.

Geographic Distribution

Asia and the Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants.

Clinical Presentation

Most infections are light and asymptomatic. In heavier infections, symptoms include diarrhea, abdominal pain, fever, ascites, anasarca and intestinal obstruction.

Fasciolopsis buski eggs.

 

Eggs of Fasciolopsis buski are broadly ellipsoidal, operculated and measure 130-150 µm long by 60-90 µm wide. The eggs are unembryonated when passed in feces. The eggs of F. buski can be difficult to distinguish from Fasciola hepatica, although the abopercular end of the latter often has a roughened or irregular area.
	Figure A

Figure A: Egg of F. buski in a unstained wet mount.

	Figure B

Figure B: Egg of F. buski in a unstained wet mount.

	Figure C

Figure C: Egg of F. buski in unstained wet mounts.

	Figure D

Figure D: Egg of F. buski in an unstained wet mount of stool.

	Figure D

Figure E: Higher magnification (400x) of the egg in Figure D.

Fasciolopsis buski adults.

 

Adults of F. buski measure 20-75 mm long and have poorly-developed oral and ventral suckers. Adults reside in the intestine of the mammalian host.
	Figure B

Figure B: Adult fluke of F. buski.

	Figure A

Figure A: Adult fluke of F. buski. Image contributed by Georgia Division of Public Health.

Intermediate hosts of F. buski.

 

Fasciolopsis buski requires a snail intermediate host for completion of its life cycle. The snails used by F. buski are small planorbid snails in the genera Hippeutis and Segmentina.
	Figure A

Figure A: Snail in the genus Hippeutis, an intermediate host for F. buski. Image courtesy of Conchology, Inc, Mactan Island, Philippines.

	Figure B

Figure B: Snail in the genus Segmentina, an intermediate host for F. buski. Image courtesy of Conchology, Inc, Mactan Island, Philippines.

Laboratory Diagnosis

Microscopic identification of eggs, or more rarely of the adult flukes, in the stool or vomitus is the basis of specific diagnosis. The eggs are indistinguishable from those of Fasciola hepatica.

Morphology

Morphologic comparison with other intestinal parasites

Treatment Information

Praziquantel , adults, 75 mg/kg/day orally in three divided doses for 1 day; the dosage for children is the same.

(Note: praziquantel should be taken with liquids during a meal.)

*Not FDA-approved for this indication

Praziquantel

Oral praziquantel is available for human use in the United States.

Praziquantel is pregnancy category B. There are no adequate and well-controlled studies in pregnant women. However, the available evidence suggests no difference in adverse birth outcomes in the children of women who were accidentally treated with praziquantel during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. For individual patients in clinical settings, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Praziquantel is excreted in low concentrations in human milk. According to WHO guidelines for mass prevention campaigns, the use of praziquantel during lactation is encouraged. For individual patients in clinical settings, praziquantel should be used in breast-feeding women only when the risk to the infant is outweighed by the risk of disease progress in the mother in the absence of treatment.

The safety of praziquantel in children aged less than 4 years has not been established. Many children younger than 4 years old have been treated without reported adverse effects in mass prevention campaigns and in studies of schistosomiasis. For individual patients in clinical settings, the risk of treatment of children younger than 4 years old who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.
References
  • Keiser J, Utzinger J. The drugs we have and the drugs we need against major helminth infections. Adv Parasitol 2010;73:197-230.
  • Sripa B, Kaewkes S, Intapan PM, Maleewong W, Brindley PJ. Food-borne trematodiases in Southeast Asia epidemiology, pathology, clinical manifestation and control. Adv Parasitol 2010;72:305-50.
  • Keiser J, Utzinger J. Food-borne tremadodiases. Clin Microbiol Rev 2009;22:466-83.
  • WHO, 2009. WHO Model Formulary. In: World Health Organization. WHO Press, Geneva.
  • Keiser J, Utzinger J. Chemotherapy for major food-borne trematodes: a review. Expert Opin Pharmacother 2004; 5: 1711–26.
  • Graczyk TK, Gilman RH, Fried B. Fasciolopsiasis: is it a controllable food-borne disease? Parasitol Res 2001;87:80-3.

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: May 3, 2016
  • Page last updated: May 3, 2016
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