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 stool The 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 , rediae The 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: Egg of <em>F. buski</em> in a unstained wet mount.

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

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

Figure B: Egg of <em>F. buski</em> in a unstained wet mount.

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

Figure C: Egg of <em>F. buski</em> in unstained wet mounts.

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

Figure D: Egg of <em>F. buski</em> in an unstained wet mount of stool.

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

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: Adult fluke of F. buski.

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: Snail in the genus Hippeutis, an intermediate host for <em>F. buski</em>. Image courtesy of Conchology, Inc, Mactan Island, Philippines.

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

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

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

Treatment information for fascioliasis can be found at: https://www.cdc.gov/parasites/fasciolopsis/health_professionals/index.html

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

Page last reviewed: December 8, 2017

Content source: Global Health, Division of Parasitic Diseases and Malaria