Which one of the following is an actively swimming, free-living, and non-feeding stage of the liver fluke? A. Sporocyst B. Rediae C. Cercaria D. Metacercaria
Hint: Live fluke, also known as Fasciola hepatica, is a group of parasites that comes under the class Trematoda and phylum Platyhelminthes.
Complete Answer: Liver flukes are mainly the parasites of the liver of various mammals, including humans, and causes diseases like Fascioliasis. The body is leaf-like and flattened and is covered with tegument. Fasciola hepatica is one of the largest flukes. They have oral suckers located at the end of a cone- shape projection at the anterior end and the acetabulum, a larger sucker, is also present at the anterior end.
Life cycle: - The embryonated eggs are released by the adult liver fluke into the environment through feces. Eggs become embryonated in water. - Miracidia hatch from eggs and penetrate inside the body of snails which acts as the intermediate host. There they grow to form different types of larva: sporocysts, rediae, and cercariae. - Cercariae is a free-swimming larva and has a long tail. It, then, leaves the snail and moves on aquatic vegetation, where it forms a cyst called metacercariae. - The metacercariae are present on vegetation and are ingested by ruminant animals and humans, the definitive hosts. The larva has a rigid hard outer layer, which sustains them and helps them to live longer. This stage is the infective one. It can also reach the human body through contaminated fishes. - Immature flukes excyst in the duodenum, and then penetrate the intestinal wall. After entering the liver cells, the parasite starts feeding the liver cells. After causing a lot of tissue damage, they migrate through liver parenchyma to the bile duct and transform into adult flukes.
Among the given options, C is correct, ‘Cercaria’.
Note: Miracidia is the first stage to be actively swimming and non-feeding but because it is not given in the option and the next stage is Cercaria, which is also free-swimming.