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 (<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 at grazing
- 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