Question

Choose the stage that infects the intermediate and definitive host of Fasciola, respectively:

• A. Miracidia, Metacercariae
• B. Metacercariae, Miracidia
• C. Miracidia, Rediae
• D. Rediae, Miracidia

Answer 1

The correct option is A Miracidia, Metacercariae

Fasciola hepatica is a flat worm and belongs to the phylum Platyhelminthes. It is also known as common liver fluke or sheep liver fluke. It causes the rotting of liver in sheep. It has two hosts: definitive and intermediate. The sexual maturity of the parasite is gained in the body of the definitive hosts such as ruminants and humans. Several asexual stages are seen in the body of the intermediate host such as snails.

The life cycle begins when the immature eggs in the stool of the infected organism is passed out. the eggs become embryonated in water in about 2 weeks. Embryonated eggs release miracidia. Miracidia is a ciliated, non-feeding larva and it infects the intermediate host (snail). In the snail, the parasites undergo several developmental stages: Sporocysts form Rediae and Rediae forms Cercariae. The cercariae are then released from the snail and they form a cyst around them. This stage is known as Metacercariae and is usually found on the aquatic vegetation.

Humans and other mammals such as Sheep, which are the definitive hosts, become infected by ingesting metacercariae-contaminated vegetation. These immature flukes migrate to the liver. They mature into adult flukes and then produce eggs. these eggs are passed through the stool.

Hence, Miracidia and Metacercariae are the stages of the Fasciola that infects the intermediate and the definitive hosts, respectively.