Human echinococcosis is a zoonotic disease caused by tapeworms of the genus Echinococcus. Humans are infected through ingestion of parasite eggs in contaminated food, water, or soil, or through direct contact with animal hosts. The larval stage of the species Echinococcus granulosus migrates to various tissues such as liver, lungs, spleen, muscle, brain, and kidneys and produces large a fluid-filled cyst called Hydatid cyst (cystic echinococcosis). The photograph shows a large hydatid cyst in the liver of a 59 y/o female. It is filled with membranous structures. Image copyright: pathorama.ch.