Class Digenea

Morphologically, digeneans differ from monogeneans in having two suckers - an anterior oral sucker and a ventral sucker called an acetabulum. All digeneans are monoecious (each individual having both testes and ovaries), with the exception of the blood flukes which are dioecious (having separate sexes).

They parasitize all classes of vertebrates, especially fishes. All digenean species have at least two hosts, the first a mollusc. In domestic animals and humans, they cause considerable economic losses and suffering.

Fasciola hepatica (sheep liver fluke)

Adults lay non-embryonated, operculated eggs which will pass from the bile ducts of the liver into the alimentary tract. These will eventually pass out into the environment with the host feces. After an initial development time, a free living ciliated larva (miracidium) will break out of the egg into a water environment. These miracidium will seek out and penetrate a snail host. After penetrating the host, the miracidium will shed its cilia and develop into a sporocyst (bag-like creature). Inside the sporocysts will develop new larval flukes called redia. These redia will have daughter redia developing inside them. Within the daughter redia will develop the cercariae, which will finally escape from the snail and become free-swimming. When a cercaria reaches vegetation, its "tail" will be dropped, it will encyst on the plant and an infective metacercaria will develop.

Grazing animals will now ingest the metacercaria and the emerging larva will migrate through the intestine, eventually to reach the bile ducts where it matures to an adult liver fluke.

Besides cattle and sheep, horses, rabbits, goats, pigs, dogs, squirrels, and humans can become infected with F. hepatica.

Eating raw F. hepatica-infected liver may cause a condition known as halzoun. This is a condition of hoarseness, irritation and coughing caused by young flukes becoming attached to the pharyngeal membranes.

Examine the slides of the life cycle of F. hepatica.

Anterior end of adult (from WWW)
Egg (from WWW)
Miracidium (from WWW)
Redia (from WWW)
Cercaria (from WWW)
Miracidium (UCD slide)
Anterior end of adult (UCD slide)
Area of ootype (UCD slide)
Vitellaria (UCD slide)
Ovary (UCD slide)
Egg (UCD slide)
Egg (UCD slide)
Redia (UCD slide)
Sporocyst (UCD slide)
Sporocyst (UCD slide)
Redia (UCD slide)
Redia (UCD slide)
Redia (UCD slide)
Redia (UCD slide)
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