fasciola

Fasciola is a genus of parasitic flatworms in the class Trematoda, commonly called liver flukes. The two principal species that infect humans and other mammals are Fasciola hepatica, the common liver fluke, and Fasciola gigantica, the great liver fluke. They inhabit the bile ducts of the liver in definitive hosts such as sheep, cattle, and humans, and their life cycle requires freshwater snails as intermediate hosts.

Life cycle: Eggs shed in bile and feces reach freshwater, where they hatch into miracidia that infect freshwater snails of the genus Lymnaea. Inside the snail, the parasites develop through several stages and emerge as cercariae that form metacercariae on aquatic vegetation. Humans and other mammals become infected by ingesting metacercariae on waterplants or with contaminated water. After ingestion, immature flukes penetrate the gut wall, migrate through the liver parenchyma to the bile ducts, and mature into adults.

Clinical features: Fascioliasis has an acute migratory phase with fever, right upper quadrant pain, hepatomegaly, and eosinophilia as larvae traverse the liver. A chronic phase follows, with biliary obstruction, cholangitis, and possible pancreatitis; adults reside in the bile ducts and may cause biliary disease.

Diagnosis and treatment: Diagnosis relies on serology and imaging during the acute phase, and on stool examination for Fasciola eggs once adults are present in the bile ducts. The eggs are large, golden-brown, ovoid, and have an operculum. The drug of choice is triclabendazole; bithionol and nitazoxanide may be used in some settings as alternatives.

Prevention and epidemiology: Fasciola is a zoonotic parasite with a worldwide distribution, especially in regions with sheep or cattle farming. Prevention focuses on avoiding ingestion of contaminated water or vegetables, along with snail control and proper water treatment.