Question

The lifecycle of Fasciola hepatica involves which intermediate host?

• A. Human
• B. Snail
• C. Cow
• D. Fish

Answer 1

Answer:

B. Snail

Fasciola hepatica Lifecycle and Key Facts

• Fasciola hepatica, commonly known as the common liver fluke or sheep liver fluke, is a parasitic trematode (flatworm) belonging to the phylum Platyhelminthes. It primarily infects the bile ducts and liver of various mammals, especially ruminants like sheep, cattle, and goats.
• Its lifecycle is digenetic, meaning it requires two different hosts to complete its development: an intermediate host and a definitive host.

• Intermediate Host: Snail

  • The intermediate host for Fasciola hepatica is a freshwater snail, most commonly from the genus Lymnaea, particularly Lymnaea truncatula (also known as Galba truncatula in some classifications).
  • In the snail, several larval stages develop and multiply asexually:
    • Miracidium: Hatches from eggs in water and infects the snail.
    • Sporocyst: Develops from miracidium inside the snail.
    • Redia: Develops from sporocyst, also inside the snail, and produces more rediae or cercariae.
    • Cercaria: Tadpole-like larvae that emerge from the snail and swim in water.

• Definitive Host: Mammals (e.g., Sheep, Cattle)

  • The definitive host is typically a grazing herbivore, like sheep, cattle, or sometimes humans, where the adult fluke resides and sexually reproduces.
  • Metacercariae: Cercariae encyst on aquatic vegetation (e.g., grass) to form metacercariae, which are the infective stage for the definitive host.
  • When the definitive host ingests metacercariae, they excyst in the duodenum, penetrate the intestinal wall, migrate through the peritoneal cavity, and eventually reach the liver bile ducts, where they mature into adult flukes.
• The disease caused by Fasciola hepatica infection is called fascioliasis or liver fluke disease, which can lead to significant economic losses in livestock due to reduced productivity and liver condemnation.
• Prevention and Control: Control measures often involve molluscicides to kill snails, deworming of livestock, and avoiding grazing in wet, marshy areas where infected snails and metacercariae are prevalent.