Dicrocoelium dendriticum

Dicrocoelium dendriticum - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Dicrocoelium dendriticum adult from horse faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

This is a small fluke (less than 1.5cm) found in the bile ducts of ruminants and some other herbivores.
The flukes migrate directly up the common bile duct to reach the bile ducts within the liver - they are therefore much less pathogenic than Fasciola (which burrow through the liver parenchyma).
Dicrocoelium is rare in Britain, occurring mainly in the Hebrides, but is common in Europe.
Small dark-brown eggs are shed in faeces.
These contain a miracidium.
If ingested by a land snail, the flukes develop, forming cercariae.
These are excreted by the snails in slime-balls, which are collected and eaten by wood-ants.
Metacercariae form inside the ants.
The final host is infected when ants are eaten with grass.
The presence of metacercariae in the nerve ganglia of the ants makes them revert to a primitive behaviour pattern, whereby they cling onto herbage overnight instead of retreating to the nest.
This enhances the likelihood of being eaten by grazing animals.