Cestodes: Echinococcus granulosus (Hydatid Tapeworm Life Cycle)

Echinococcus granulosus: Hydatid tapeworm

• Typically passes its life cycle in canids (dogs, wolves, etc.) and sheep.
• Humans are accidental hosts when they ingest the eggs, which are passed in canine feces.
• Large, complex cysts form in human tissues.

– These cysts can rupture and cause anaphylactic shock and disseminate the parasites. Sheep-Candis 1. Sheep (key intermediate hosts) ingest eggs in contaminated vegetation. 2. In the sheep, the eggs release oncospheres; the oncospheres travel to other tissues. 3. In those tissues, oncospheres form cysts. 4. The definitive hosts, canids, ingest infected sheep meat. 5. In the host, the cysts give rise to adult forms, which produce eggs. 6. Eggs are passed in the feces. Humans 7. Humans can accidentally ingest eggs in canid feces. 8. The eggs release oncospheres, which then travel to other tissues (just as in sheep). 9. Oncocysts form hydatid cysts in those tissues. 10. The cysts grow; they damage tissues and can rupture. Other species of Echinococcous* cause alveolar echinococcosis, polycystic echinococcosis. https://www.cdc.gov/dpdx/echinococcosis/index.html