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[Echinococcus granulosus] [Echinococcus multilocularis] [Echinococcus oligarthrus] [Echinococcus vogeli]

Dogs and other canids are the definitive hosts for Echinococcus spp.; humans are are only infected by the larvae after ingestion of eggs from food, water or fomites contaminated with dog feces.  Upon ingestion of the eggs by the human host, the oncospheres migrate from the intestinal lumen to other body sites and develop into hydatid cysts.  These cysts can be found in any part of the body, but are most common in the liver, lung and central nervous system.

A	B

A: Protoscoleces in a hydatid cyst removed from lung tissue, stained with hematoxylin and eosin (H&E).  Image taken at 200x magnification.  Image courtesy of Phoenix Children's Hospital, Phoenix, AZ.
B: Higher magnification (600x) of the protoscoleces in Figure A.

C	D

C: Cross-section of an E. granulosus cyst, stained with H&E.  The cyst wall is composed of an acellular laminated external layer (green arrow) and a thin, germinal (nucleated) inner layer (yellow arrow).  Note the brood capsule (black arrow) with protoscoleces (blue arrows) inside.  Image taken at 40× magnification.
D: Higher magnification (200×) of the cyst in Figure C, showing daughter cyst (brood capsule).  Note the hooklets (purple arrow) inside one of the protoscoleces and the calcareous corpuscles (light blue arrows) along the germinal layer.

E	F

E, F: Protoscoleces liberated from a hydatid cyst.