Cycles

Lancet Flukes
(Dicrocoelium lanceolatum)

Lancet flukes are found throughout Europe, the Middle East, Asia, Africa, North and South America and Australia. The parasite tends to be found in areas that favor the primary hosts, such as fields. Much of what is presently known about lancet flukes is the result of the work of the naturalist Wendell Krull.

The lancet fluke’s final host is a cow, but it goes through a cycle of cow, snail, and ant. This cycle repeats when the newly matured lancet flukes lay eggs in the cows stomach.

Cause

Snails eat the dung from the cow becoming infected by the flukes; the flukes will then dig through the snail’s digestive tract into the gland that creates slime. As the snail moves, their infected slime covers whatever it comes into contact with. The next carrier for the flukes is the ant which eats the slime the snails leave behind. The flukes then begin their mind control on the ants. To all the other ants, the infected ant is normal. It collects food and does other normal ant-like things. If the colony knew that the ant was infected it would be unable to stay as a part of the colony. But at night, the infected ant climbs a blade of grass and waits to be ingested by a cow. If the ant is not digested by a cow the parasite makes the ant climb the blade of grass every night until it is. When the ant is finally swallowed, it is drowned in cud, bursting open as a swarm of flukes infect the cows stomach, the flukes complete the cycle by penetrating the cow’s liver, they then become adult egg producers. Lancet flukes also infect sheep as their primary host.

In Humans

Due to the specific nature of this parasite’s life cycle, human infections are generally rare. But, humans and other herbivorous mammals can also become primary hosts through ingestion of infected ants.

Symptoms in humans

Symptoms can include biliary colic and other digestive disturbances; including bloating and diarrhea. In heavier infections inflammation of the liver may occur.

Lancet fluke in liver

Sources
http://www.damninteresting.com/a-fluke-of-nature
http://www.answers.com/topic/lancet-fluke