Facts About Liver Fluke

The term "liver fluke" is applied to two distinct species of parasitic flatworms (also known as trematodes) whose hosts include freshwater snails and herbivorous (plant-eating) mammals, particularly livestock such as cattle, sheep and goats. Liver flukes can also infect humans. Though a small scale infection may pass relatively unnoticed, large numbers of liver flukes can cause severe liver damage and even death. Fortunately, the symptoms of Fascioliasis (liver fluke infection) are well documented and treatments are available.

  1. Species

    • The two species of liver fluke are Fasciola hepatica and Fasciola gigantica. The latter is named for its larger size (approximately two to three times that of the hepatica). Both species are widely dispersed, with hepatica infections reported on every continent except Antarctica. Liver flukes thrive in environments in which hosts are readily available, namely areas where significant quantities of water and livestock can be found.

    Life Cycle

    • After hatching from eggs in fresh water, a larval form of the liver fluke known as a miracidia penetrates the shell of a snail. While inside its intermediate host, the miracidia changes into a cercaria, a free-swimming larva with a tail. After leaving the snail, the cercaria encloses itself in a cyst on a blade of grass or even the surface of the water, where it is then consumed by its next host. Once inside a mammal, the cercaria burrows through the intestines, eventually boring into the liver to lay its eggs. These eggs, in turn, are expelled with the animal's waste, completing the liver fluke's life cycle.

    Symptoms of Liver Fluke Infestation

    • Symptoms of a severe liver fluke infection (in which multiple flukes attack the liver roughly simultaneously) include rapid weight loss, jaundice and diarrhea. In cattle, decreased fertility is another sign that liver flukes may be present.

    Liver Flukes in Humans

    • Though humans are not the primary host of liver flukes, infection can occur by drinking contaminated water or consuming uncooked aquatic plants such as watercress. Inside a human host, a cercaria typically takes three to four months to mature into an adult liver fluke, at which time it will proceed to the liver to lay its eggs.

    Treatment

    • A number of drugs designed to kill liver flukes in various species can be found on the market. Clorsulon, sold commercially under the name Curatrem, is used to treat liver fluke infection in cattle. Triclabendazole, sold in tablet form as Egaten, is safe for human use.