Fasciola hepatica is a Platyhelminthic flatwork known as the liver fluke of sheep. It has been an important parasite of sheep and cattle for hundreds of years. People become infected from eating plants from wet places, such as watercress. Fasciola hepatica can cause fever, liver damage, and may make its way into the brain.
Fasciola hepatica is ingested on a water plant in the metacercaria stage. The metacercaria excysts in the duodenum and penetrates the intestinal wall. It moves through the abdominal cavity and penetrates the liver. The adults are found in the bile duct. Unembryonated eggs leave the body in feces. The egg embryonates in water. The miracidium hatches and penetrates a snail. A sporocyst forms in the snail tissue and becomes a redia.The cercaria are free swimming and settle on a water plant to become a metacercaria.
Damage is done when the fluke migrates through the liver and feeds on liver cells and blood, which can cause anemia in heavy infections. Worms in the bile duct cause inflammation and edema, limiting their capacity and causing them to be less responsive to the liver. This causes backpressure and can lead to atropy of the liver parenchyma, cirrhosis, and jaundice. In heavy infections the bile duct is eroded completely and the gall bladder is damaged.