The eggs then rupture in a damp environment (pastures) and the larvae, known as miracidia, grow rapidly, reproducing through an asexual mechanism within small aquatic molluscs, limnaea. The new larvae are called cercariae. Each miracidium can produce 1,000 to 10,000 cercariae.
These take on a swimming form and, in autumn, bind to various plant supports by positive phototropism. This infesting form is known as the metacercariae.
Herbivores are infected by eating infested plants. The metacercariae rupture in the gastro-intestinal tract and the small flukes grow whilst they move along the gastro-intestinal mucosa, then cross it arriving in the liver and entering Glisson's capsule before reaching the bile ducts where the mature flukes become established and re-start the cycle.
Human beings can be infested by eating dandelions, cress, or other wild salad leaves.
The disease is asymptomatic in approximately 25% of cases.
These symptoms may add to each other or they may be present in part.
Flukes implanted in a deer liver Source: AFFSA.