Digenea

Digenea is a class of trematodes in the phylum Platyhelminthes, with about 6,000 species. The name "Digenea" derives from the Greek "dis", meaning "double", and "genes", meaning "born". It refers to the two-host life cycle of the parasites, involving a definitive host and one or two intermediate hosts.

Taxonomy

The Digenea are one of the three major groups of parasitic platyhelminths, the others being the Monogenea and Cestoda. The Digenea are endoparasites in the digestive tract, respiratory tract, circulatory system, or other organs of vertebrates, including humans and other mammals, birds, and fish.

Life Cycle

The life cycle of a typical digenean begins with the release of eggs from the definitive host into the environment. The eggs hatch in water to release a free-swimming larva, the miracidium, which infects the first intermediate host, typically a snail. Inside the snail, the miracidium transforms into a sporocyst or redia, in which further asexual reproduction occurs, producing either more rediae or cercariae. The cercariae are released from the snail and encyst as metacercariae in the second intermediate host or in the environment. The definitive host is infected by eating the second intermediate host or the encysted metacercariae.

Morphology

Digeneans are flattened and leaf-like or cylindrical. The anterior end is a holdfast organ, the oral sucker, surrounding the mouth. The posterior end may have a second holdfast, the ventral sucker or acetabulum. The skin is covered with tiny spines, which may be scale-like and overlapping, or rod-like or conical.

Pathology

Digenean infections, known as digenean trematode infections, can cause a variety of diseases in humans and other animals, including schistosomiasis, fascioliasis, clonorchiasis, opisthorchiasis, and paragonimiasis.

See Also

• Trematoda
• Parasitology
• Helminthiasis

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