Hydatid cyst in liver. Gross specimen of a cyst in a patient's liver, arising from infestation with the eggs of the tapeworm parasite Echinococcus granulosus. Humans are not a natural host of the parasite, but may become infected by ingesting eggs in food that has been contaminated by the faeces of an infected animal, usually a sheep or a dog. Cysts may be formed in the lungs, brain, liver or kidneys. Each cyst contains thousands of larvae. If ruptured, spread of the parasite will occur. Treatment is either with the surgical removal of the cysts, or sterilizing and draining them.