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Dicrocoeliasis

[Dicrocoelium dendriticum]

Causal Agents

The trematode Dicrocoelium dendriticum, the lanceolate fluke.


Life Cycle

lifecycle

Ruminants are the usual definitive hosts for Dicrocoelium dendricitum, although other herbivorous animals, carnivores, and humans can serve as definitive hosts. Embryonated eggs are shed in feces The Number 1. The eggs are ingested by a snail The Number 2. Many species of snail may serve as the first intermediate host, including Zebrina spp. and Cionella spp. When the miracidia hatch The Number 2a, they migrate through the gut wall and settle into the adjacent vascular connective tissue, where they become mother sporocysts The Number 2b. The sporocysts migrate to the digestive gland where they give rise to several daughter sporocysts. Inside each daughter sporocyst, cercariae are produced The Number 2c. The cercariae migrate to the respiration chamber where they are shed in slime ball from the snail The Number 3. After a slime ball is ingested by an ant, the cercariae become free in the intestine and migrate to the hemocoel where they become metacercariae The Number 4. Many ants may serve as the second intermediate host, especially members of the genus, Formica. After an ant is eaten by the definitive host The Number 5, the metacercariae excyst in the small intestine. The worms migrate to the bile duct where they mature into adults The Number 6. Humans can serve as definitive hosts after accidentally ingesting infected ants The Number 7.

Geographic Distribution

Europe, northern Asia, America and northern Africa.

Clinical Presentation

Most infections are light and asymptomatic. In heavier infections, symptoms may include cholecystitis, liver abscesses and upper abdominal pain.

Dicrocoelium dendriticum eggs in wet mounts.

 

Eggs of Dicrocoelium dendriticum are operculated and measure 35-45 µm long by 20-30 µm wide. The eggs are thick-shelled and usually dark brown in color. Eggs are fully embryonated when shed in feces.
	Figure A

Figure A: Egg of Dicrocoelium dendriticum in an unstained wet mount of stool. Image courtesy of Dr. Juan Cuadros González.

	Figure B

Figure B: Egg of Dicrocoelium dendriticum in an unstained wet mount of stool. Image courtesy of Dr. Juan Cuadros González.

	Figure C

Figure C: Egg of Dicrocoelium dendriticum in an unstained wet mount of stool. Image courtesy of Dr. Juan Cuadros González.

	Figure D

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

	Figure E

Figure E: Egg of D. dendriticum in an unstained wet mount of stool.

Dicrocoelium dendriticum adults.

 

Adults of Dicrocoelium dendriticum are flattened and taper at both the anterior and posterior ends. The paired testes lie just behind the anteriorly-located ventral sucker (acetabulum). The ovary is small and located behind the testes. Adults reside in the bile ducts of the definitive host.
	Figure A

Figure A: Adult of D. dendriticum, stained with carmine. Structures illustrated in this figure include: oral sucker (OS), acetabulum (AC), uterus (UT), testes (TE), and vitelline glands (VT).

Intermediate hosts of Dicrocoelium dendriticum.

 

Like all trematodes, Dicrocoelium dendriticum requires a snail as a first intermediate host. Over 50 species of land snail may serve as the first intermediate host. The second intermediate host is an ant, usually in the genus Formica, although other genera may serve as a host.
	Figure A

Figure A: Zebrina detrita, a common first intermediate host for D. dendriticum. Image courtesy of Conchology, Inc, Mactan Island, Philippines.

	Figure B

Figure B: Formica fusca, a common second intermediate host for D. dendriticum in Europe. Image courtesy of Sedeer El-Showk.

Laboratory Diagnosis

Microscopic identification of eggs in the stool or duodenal fluid. If eggs are found only in stool, it could represent spurious passage following the ingestion of infected animal liver. Additional specimens should be collected to confirm a true infection.

Morphologic comparison with other intestinal parasites

Treatment Information

In humans, the diagnosis of dicrocoeliasis is typically spurious based on parasite eggs that are passed in the feces after consumption of infected animal liver. True infections are rare. Infection has been treated successfully with praziquantel, 25 mg/kg three times orally daily for 2 days. Praziquantel is not approved for treatment of children less than 4 years old. Niclosamide is effective but is not available in the United States.

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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