The Life Cycle of Fasciola

The liver fluke is a parasitic worm that infects many mammalian hosts, most notably sheep and humans. The adult worm has a very definitive leaf shape, with the head region being significantly wider than the rear. The worm comes equipped with very powerful suckers that help it attach to the structures in the liver, mainly the biliary ducts. These worms are hermaphroditic, meaning they reproduce asexually.

  1. Reproduction

    • Adult liver flukes reside in the biliary ducts of the liver and can fertilize and discharge their own eggs, making sexual reproduction unnecessary. The immature eggs are discharged out of the biliary ducts and into the environment through the feces of the primary host. The eggs require water in order to hatch into infective larvae.

    Development

    • After hatching, the immature larvae of the liver fluke, called the miracidium, infects a snail as an intermediate host, where several stages of development occur (sporocysts, rediae, and cercariae). It is at this point that the larvae are ready to infect a new primary host.

    Intermediate Host

    • The cercariae are released from the snail through its feces and are re-released into the environment, where they go dormant in a cyst form and await ingestion from a new primary host. These cysts will remain viable on the vegetation for several years.

    New Primary Host Infection

    • The new primary host will ingest the cysts along with the vegetation and continue the development cycle of the fluke. The metacercariae will become active again in the duodenum during the digestive process and will migrate through the intestinal wall, the abdominal cavity and then into the liver, where it will take up residence and continue to mature. This maturation process will take from three to four months in humans, though in other mammals, the process could take more or less time to complete.

    Treatment

    • The good news is that humans with liver fluke infections can expect a recovery rate of 80% to 100% with the use of oral medication protocols, namely bithinol. Triclabendazole is also being used successfully to treat liver fluke infections. It is quickly becoming the drug of choice since the dosage is considerably lower, the treatment protocol is shorter and the cost is less.