Ciclo de Vida de Fasciola Hepatica

Fasciola Hepatica: Life Cycle

Overview

Fasciola hepatica is a trematode parasite that causes liver fluke disease (fasciolosis) in animals and humans. The disease is most pathogenic in sheep, and its complex life cycle involves an intermediate host, the mud snail, and several free-living stages.

Life Cycle Stages

1. Adult Flukes: Adult flukes live in the bile ducts of the liver, where they feed on blood and other tissue secretions. They lay eggs that are passed out onto pasture in the faeces.
2. Hatching: At suitable temperatures (greater than 10ºC), a miracidium develops within the egg and hatches, migrating in thin films of moisture to actively seek the snail host. Miracidia can only survive for a few hours outside the snail.
3. Inside the Snail: Within the snail, the miracidia undergo two further developmental stages, including multiplication, eventually becoming infective cercariae. Cercariae emerge from the snail when the temperature and moisture levels are suitable.
4. Infective Stage: The cercariae migrate onto wet herbage, encysting as metacercariae, the highly resilient infective stage of the liver fluke. Following ingestion, the young flukes migrate to the liver, through which they tunnel, causing tissue damage.
5. Patent Infection: The infection is patent about 10-12 weeks after the metacercariae are ingested. The whole cycle takes 18-20 weeks.

Environmental Factors

The lifecycle of Fasciola hepatica is influenced by environmental factors such as moisture and temperature. The hatching of fluke eggs and the multiplication of snails depend on adequate moisture and temperatures greater than 10ºC. The incidence of fasciolosis is highest in years when rainfall is above average during May, June, and July.

Clinical Forms

Liver fluke disease in sheep occurs in three main clinical forms: acute, subacute, and chronic fasciolosis. The form depends on the numbers of infective metacercariae ingested and the period of time over which they are ingested. Recent milder winters and wetter summers have seen patterns in parasite epidemiology change, with earlier seasonal reports of acute disease.

Prevention and Treatment

Prevention strategies include reducing the incidence of snails and controlling their breeding, avoiding grazing in pastures contaminated with fluke eggs, and administering prophylactic anthelmintic treatments. Treatment typically involves the use of triclabendazole, which effectively kills the liver flukes and their eggs. Other drugs may be used to treat some of the symptoms such as pain and diarrhea, and surgery may be necessary in rare cases where cholangitis, an infection of the bile ducts in the liver, has developed.