Metacercariae

Detailed article on Metacercariae

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Metacercariae
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Trematoda
Order:
Family:	'

Metacercariae are the encysted larval stage of certain parasitic trematodes, commonly known as flukes, which are part of the class Trematoda within the phylum Platyhelminthes. This stage is crucial in the life cycle of these parasites, as it represents the form that is typically infective to the definitive host.

Life Cycle

The life cycle of a typical trematode involves several stages:

1. Eggs: The life cycle begins when eggs are released into the environment, often through the feces of the definitive host.
2. Miracidium: The eggs hatch into free-swimming larvae called miracidia, which must find and penetrate a suitable intermediate host, usually a snail.
3. Sporocyst and Redia: Inside the snail, the miracidia transform into sporocysts, which then produce rediae. These stages multiply asexually within the snail.
4. Cercariae: The rediae give rise to cercariae, which are free-swimming larvae that leave the snail to find a second intermediate host or encyst on vegetation.
5. Metacercariae: The cercariae encyst to form metacercariae, which are the infective stage for the definitive host. This stage can occur in a second intermediate host, such as a fish or crustacean, or on aquatic vegetation.
6. Adult Fluke: Once ingested by the definitive host, the metacercariae excyst in the host's digestive tract, migrate to their target organ, and mature into adult flukes.

Morphology

Metacercariae are typically spherical or oval in shape and are encased in a thick cyst wall that provides protection in the external environment or within the tissues of the intermediate host. The cyst wall is composed of several layers, which can vary in thickness and composition depending on the species.

Infection and Pathology

Infection with metacercariae occurs when the definitive host ingests contaminated water, vegetation, or intermediate hosts harboring the encysted larvae. Once inside the host, the metacercariae excyst and migrate to their specific site of infection, such as the liver, lungs, or intestines, where they develop into adult flukes.

The pathology associated with metacercarial infection depends on the species of trematode and the site of infection. Common symptoms include abdominal pain, diarrhea, and in severe cases, organ damage and dysfunction.

Prevention and Control

Preventing infection with metacercariae involves controlling the intermediate hosts, such as snails, and ensuring that food and water are free from contamination. Cooking food thoroughly and avoiding raw or undercooked aquatic products can reduce the risk of infection.

Also see

• Trematoda
• Platyhelminthes
• Parasitology
• Helminthiasis
• Intermediate host