Dicrocoelium dendriticum: Lancet fluke

General Description: Small, transparent flukes, 6 to 10mm long and 1.5 to 2.5mm 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.

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 ducts during their development to the adult stage. The prepatent period is about 11 weeks.

Location: Bile ducts of liver.

Geographical Distribution: Europe, Asia and North America.

Significance: Damage is not as great as with Fasciola hepatica, but is severe infections there may be extensive hepatic cirrhosis and distension of the bile ducts. Sheep which are diseased with heavy infections may become unthrifty.

Effect on Host: 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, edema and weight loss.

Diagnostic Information: Brown eggs containing a miracidium may be found in faeces.

Control: Control is difficult for several reasons. Dicrocoelium eggs remain infective for months in soil and faeces; 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.

 

Dirocoelium dendriticum – adults