Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
a tapeworm that in the adult stage parasitizes the intestines of dogs, wolves, jackals, and occasionally cats. The body measures 3–5 mm in length and consists of a scolex with four suckers and two crowns of hooks and three or four segments. The last segment, the only mature section, constitutes half the body length.
The tapeworm’s eggs emerge from the host’s intestine with excrement and may remain on its fur. The intermediate host, which may be a cow, sheep, pig, or other animal, or a human being, becomes infested by swallowing the eggs. The larva (oncosphere) emerges from the egg while in the intestine of the intermediate host. It penetrates into the portal vein system through the intestinal wall and is carried by the blood to the liver or, in some cases, to the lungs, muscles, bones, and other organs, where it develops into a hydatid. Every oncosphere creates a cyst, and secondary and tertiary cysts form on its walls. Numerous scolices similar to those of adult worms form on the secondary and tertiary cysts. The cysts grow very slowly and become quite large. The definitive host becomes infected by eating the flesh of a diseased or dead animal and ingesting a worm in the hydatid stage.
The varied structure of the hydatid stages of E. granulosus suggests there may be two independent species, E. unilocularis and E. multilocularis. The latter is sometimes recognized as an independent genus, Alveococcus.