Fluke Life Cycle

Most flukes of cattle follow this basic indirect life cycle that involves an intermediate freshwater snail host either a lymnaeid snail (liver fluke, Fasciola hepatica) or a planorbid snail (stomach flukes, Paramphistome species).

Dung stage

Fluke eggs containing a triangular-shaped miracidium are passed in the dung.

• Eggs deposited in water quickly become free of dung.
• Eggs hatch when water temperatures are suitable.

The released free-swimming miracidium must invade a snail host within 24–30 hours, otherwise it dies.

Intermediate host stage: aquatic snails

Intermediate fluke stages develop and multiply in lymnaeid (liver fluke) or planorbid (stomach fluke) snails.

• The miracidium develops through a number of stages. Each stage involves the fluke multiplying itself.
• A sporocyst divides to produce ‘daughter’ sporocysts.
• Sporocysts divide to produce a maximum of eight rediae.
• Rediae divide to produce cercariae.
• The tadpole-like cercariae exit the snail host.

Pasture stage in wet areas: spreading of infection

• Cercariae swim to disperse then settle onto vegetation within 24 hours otherwise they die.
• They lose their tails then secrete a protective cyst covering to become metacercariae.
• The metacercariae are very resistant to cold and heat, and especially to dry conditions.

Final host stage in cattle: new infection and re-infection

Naïve cattle are infected by ingesting metacercariae on the pasture. Uneaten cysts die.

After being ingested by cattle,

• Metacercariae hatch into juvenile flukes in the small intestine:
  • Juvenile liver flukes penetrate the gut wall and move with the blood to the liver and then to the bile ducts to develop into adults.
  • Juvenile stomach flukes are retained within the small intestine and finally move back up the gut to the rumen and reticulum.