Fasciola Hepatica Life Cycle

Fasciola Hepatica, also known as the liver fluke, is a parasite that can live in mammals, including humans. It most commonly attacks cattle and sheep. The fluke grows to about 30 mm (slightly over 1 inch) in length and takes up permanent residence in the bile ducts of the liver, where it adheres to the duct walls with a powerful, sucker-like mouth. The life cycle takes two to three months under ideal conditions.

Reproduction

• Adult Fasciola Hepatica flukes contain both testes and ovaries, so they are able to reproduce independently. Each adult, once securely lodged in the liver, can produce up to 25,000 eggs per day.

Eggs

• The liver fluke eggs are passed out of the host in its feces. One infested sheep may deposit a half-million eggs per day with its droppings. Under wet conditions, each egg is washed out of the fecal matter and hatches, releasing a larva called a miricidium.

Larvae

• The liver fluke's miricidia larvae are washed by rain water into streams, where they invade aquatic snails, their next hosts. Inside the snails, they develop into three different forms of parasites, including tadpole-like cercaria.

Infectious cysts

• Cercaria exit the snails and swim until they find grass or other vegetation to which they can adhere. There they form cysts called metacercariae. This is the infectious form of the liver fluke. An animal or human who eats contaminated plant material will ingest the metacercariae.

New Host

• Within the animal or human's intestines, the metacercaria break out of their cysts as immature flukes. The flukes penetrate through the intestinal walls, enter the abdominal cavity and migrate to the new host's liver. Within a few weeks, each fluke lodges in one of the liver's bile ducts and reaches full maturity. When mature, it is ready to reproduce asexually and release new eggs.

Consequences

• Fasciola Hepatica infection is called fascioliasis. The fluke infestation disrupts the host's digestive system and can cause diarrhea. The migration of the fluke through the liver also can lead to hemorrhaging, which can cause anemia and sudden death, especially in ruminant animals such as cows and sheep. Human infection is rare, but the flukes can live and reproduce in the human bile ducts for 10 years or more, causing repeated health issues. Symptoms include fever, anemia and swollen liver. Liver flukes can lodge in the throat of people who eat infected raw liver and cause respiratory problems. Human fascioliasis is highly treatable, once diagnosed.

Prevention/Solution

• Animals living on properties where liver flukes have been a problem must be treated with an anti-parasitic medication three times per year, to catch the flukes in various developmental stages. Liver flukes are killed in the cooking process; humans can avoid fascioliasis by not eating raw shellfish or raw liver. Extra care should be taken in handling raw snails, including hand washing and sterilization of preparation surfaces after contact with raw snails.