Hydatid disease is a parasitic infestation by a tapeworm of the genus Echinococcus.

The incidence of hydatid disease in the United States is <1:1,000,000, except in Alaska, where the incidence is <1:100,000. Internationally, the incidence varies relative to the geographic region; endemic areas include countries bordering the Mediterranean Sea, the Middle East, southern South America, Iceland, Australia, New Zealand, and Africa. In these areas, cystic echinococcosis (CE) occurs at 1:100,000 to 220:100,000; alveolar echinococcosis (AE) occurs at 0.03:100,000 to 1.2:100,000. There is no true racial or gender preference for the affliction.

Hydatid disease originates with the ingestion, by an intermediate host, of the eggs of larval cestodes of the phylum Platyhelminthes (tapeworm). The eggs hatch into metacastodes, which infest the liver, lungs, muscles, and other organs.

Medically Important Species of Echinococcus

Species	Disease
Echinococcus granulosus	Cystic echinococcosis (CE)
Echinococcus multilocularis	Alveolar echinococcosis (AE)
Echinococcus vogelii	Rare infestation(s)