Hydatid cyst in a horse liver

Photograph of part of the liver from a horse. The liver has been carefully dissected to show a hydatid cyst, an immature stage in the life cycle of the tapeworm Echinococcus granulosus. The adult tapeworm, just a few millimetres long, is found in the small intestine of dogs and foxes. A wide variety of both domestic and wild animals, including humans, can act as the intermediate host for this parasite and harbour the cyst stage shown here.