Lancet Fluke Life Cycle

Lancet liver fluke (Dicrocoelium dendriticum) are parasites afflicting cattle and other farm or grazing mammals. Like many other parasitic flukes in the order Trematoda, lancet flukes have several different hosts during their life cycle, with farm animals being the terminal host. Although not common, these flukes can also afflict humans, specifically by infecting the bile ducts. The life cycle of the fluke has five distinct stages, although the incubation period of these parasites is not yet known.

  1. Morphology

    • Adult lancet flukes are flat, with tapered anterior and posterior ends. The anterior (or front) of the fluke has an oral sucker by which the fluke attaches to its hosts, and the posterior (or end) of the fluke contains sex organs. Depending on the host, lancet flukes can be in egg, larval, juvenile or adult stages. In farm animals, only the adult stage is present.

    Egg Stage

    • After adult flukes mate, eggs are excreted in the feces of the host, such as cattle or goats. These eggs remain in the feces until they are consumed by the terrestrial snail.

    First Intermediate Host

    • In the United States, the snail species Cionella lubrica eats the feces infected with lancet fluke eggs. Once consumed, the eggs hatch into larvae, which bore through the intestinal and stomach linings of the snail and lie in the digestive tract. Here they develop into the juvenile stage, and the immune defenses of the snail surround the parasite with organic walls, called cysts. These cysts are excreted by the snail in long trails of slime.

    Second Intermediate Host

    • Ants (Formica fusca in the United States) swallow the cysts while using the slime trail for moisture. Once inside the ant's digestive tract, the juveniles move throughout the ant body to mature into adults. One of the flukes migrates to the ganglion (or essentially the brain of the ant), and forces the infected ant away from the colony and onto a blade of grass. Once the ant is at the top of the grass, the fluke forces the ant to clamp it jaws to the grass and remain stationary until dawn. This creates opportunities for the ants to be eaten by the terminal host---cattle or other grazing animals.

    Terminal Host

    • When the cattle consumes the ant, the lancet flukes enter the digestive tract and make their way to the liver. They live out the remainder of their adult lives in the liver, excreting eggs through the host's fecal matter.

    Symptoms and Treatment

    • In farm animals, very few symptoms of infection with lancet flukes exist. Diagnostic testing involves identifying eggs in the feces or examination of the liver after death. Simple administration of anti-parasitic drugs such as Mirazid is needed to solve the infection.