Life cycle of Echinococcus granulosus (hydatid tapeworm) Life cycle of Echinococcus granulosus (hydatid tapeworm). The normal intermediate host (sheep) and the occasional intermediate host (human) are shown in contact with the normal final host (dog). The human can become contaminated with tapeworm eggs in fecal matter in the dog's fur. Transmission in the normal way—predation of a herbivore by a carnivore—results in development of numerous adult tapeworms in the dog intestine and passage of eggs in the stool, followed by infection of a grazing sheep. 1–6: An oncosphere hatches from an egg in the gut of a sheep or human (1). After penetration of the gut and development of a hydatid cyst in the liver (2), a daughter colony (3) is formed, with individual scoleces (hydatid sand) (4). Breaking of the cysts by the dog releases numerous scoleces, which are ingested and evert in the dog intestine (5), subsequently growing into adult worms, which produce viable eggs (6) that are passed in the dog's feces to contaminate fur or grass—the source of infection for humans and sheep. (Reproduced, with permission, from Goldsmith R, Heyneman D [editors]. Tropical Medicine and Parasitology. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.) Source: Protozoal & Helminthic Infections, Current Medical Diagnosis & Treatment 2017 Citation: Papadakis MA, McPhee SJ, Rabow MW. Current Medical Diagnosis & Treatment 2017; 2016 Available at: https://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/Books/1843/cmdt17_ch35_ef045.png&sec=135757588&BookID=1843&ChapterSecID=135757096&imagename= Accessed: November 08, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved