The immature form of a small tapeworm, Taenia echinococcus, found in dogs, wolves and jackals and from which human beings become infected, harbouring the immature parasite in the form known as hydatid cyst. (See TAENIASIS.) Diagnosis is based on clinical findings, imaging and blood testing. Treatment options depend on the site of cysts and what harm might be expected and include ‘watch and wait’, surgery to remove a cyst or cysts and ANTIHELMINTHICS.