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).
Figure 1. Cattle fluke (e.g. liver fluke, Fasciola hepatica) life cycle. Image created by Madison Mayfield
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.