Hydatid disease is caused by the dog tapeworm Ecchinococcus granulosus. The disease is globally distributed but more common in tropical areas. People can become infected by ingesting food or water contaminated with E. granulosus eggs. The larvae typically form cysts in the liver and lungs, though infection of the musculoskeletal system is rare. Hydatid cysts have three layers: an outer protective layer formed from host tissue, a middle acellular layer, and an inner layer containing parasites that can multiply to form new daughter cysts.