Atlas of livestock parasites
digitized collection of microscopical preparations

Atlas of Parasites Contents Information sources Glossary Administration

Dicrocoelium dendriticum

Category:


Species:
Endoparasite


Description:
Untitled document

Trematode

 "lancet fluke"

Distribution: Europe, Asia, and North America. 

Host: Bile ducts of domestic and wild ruminants, pigs, dogs, horses, rabbits.

Life Cycle:
Indirect life cycle requiring two intermediate hosts, a land snail and an ant. Miracidia develop in eggs on pasture but do not hatch until ingested by the snail (Zebrina and Cionella genera). The immature flukes grow and multiply in the snails. After 3 months, cercariae emerge from snails only in damp weather in slime balls ejected by the snail. These may be eaten by ants in which the flukes develop to infectivity. This takes 26 to 62 days, depending on temperature. Sheep become infected by swallowing the ants with grass. Digestion releases metacercariae which enter the common bile duct of the intestine and proceed up the bile duets during their development to the adult stage. The prepatent period is about 11 weeks.

Diagnosis: Small, transparent flukes, 6 to 10 mm long and 1.5 to 2.5 mm wide. The body is flattened, narrowed at the front, and widest behind the midpoint of the fluke, giving it roughly the shape of a lancet. A sedimentation test will detect the small, brown, operculate eggs in the feces. Brown eggs containing a miracidium may be found in feces.

Size: 38–45 × 22–30 µm 

Clinical features: In heavy infections, extensive cirrhosis of the liver can develop, leading to anemia and weight loss. Damage is not as great as with Fasciola hepatica, but in severe infections there may be extensive hepatic cirrhosis and distention of the bile duets. Sheep which are diseased with heavy infections may become unthrifty. Similar to that of Fasciola hepatica, but flukes do not migrate extensively through liver tissue. Cirrhosis and bile duct irritation occur as with common liver flukes, but damage is on a smaller scale. Red blood cells and albumin are lost in combination with a reduction in functional liver tissue, producing anaemia, oedema, and weight loss. 

Control:
Control is difficult for several reasons. Dicrocoelium eggs remain infective for months in soil and feces; they can survive freezing temperatures. Land snails and ants both inhabit dry areas and are less susceptible to chemical control than aquatic intermediate hosts. Also, wild animals such as woodchucks and rabbits become infected with lancet flukes and provide a reservoir for infection.                  


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