Echinococcus granulosus

Echinococcus granulosus is a parasitic cestode with a life cycle involving two hosts. The adult worm develops in the small intestine of dogs and other canids and the larval form (metacestode) develops mainly in the liver and lungs of numerous species of herbivorous and omnivorous intermediate hosts including sheep, cattle, swine and humans.

The E. granulosus metacestode (cyst) is unilocular, subspherical in shape and fluid-filled. The cyst is formed by an inner germinal membrane supported externally an acellular laminated layer, involved by a host-produced adventicial layer. In the germinal layer the undifferentiated cells proliferates and are responsible for the formation of the brood capsules. Inside the brood capsules there is an asexual budding process that originates the protoescoleces. Once ingested by the definitive host the protoescoleces can develop into an adult worm. When they reach the maturity the adult worms produce eggs that are voided in the faeces of the definitive host. The eggs, each containing an embryo (oncosphere), are infective to several animal species. After hatching in the stomach the eggs release the oncospheres that penetrate mucosa and reach the viscera, developing into the cyst.

The cyst is the pathogenic from of the parasite. The pathogeny is mainly due to the pressure of the cyst on the host viscera.

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