Infectious Agent

Cestode parasites of the genus Echinococcus , including E. granulosus, E. multilocularis , and others.


Ingestion of Echinococcus eggs shed in the feces of infected definitive hosts (dogs and other canids for E. granulosus ; foxes and other canids for E. multilocularis ), such as by hand-to-mouth transfer of eggs and by consumption of fecally contaminated food, water, or soil.


The two main forms of echinococcosis in humans are cystic echinococcosis (CE), which is caused by E. granulosus (also other species), and alveolar echinococcosis (AE), which is caused by E. multilocularis . CE is found in parts of the Americas (including in South American foci, such as in Peru), Eurasia, Africa, and Australia—including in pastoral and rangeland areas, where transmission often is maintained by dog–sheep–dog cycles. AE is found in the northern hemisphere, in parts of Eurasia and North America. Although indigenous human cases of CE and AE have been reported in the United States, most US cases of echinococcosis have been imported.

Clinical Presentation

People with CE and AE may remain asymptomatic for years. The nature and severity of the clinical manifestations depend in part on the location, size, and other characteristics of the lesions that develop and the associated complications. In CE, the lesions are cystic (referred to as hydatid cysts) and most commonly develop in the liver; the next most common site is the lungs, but cysts may develop in other organ systems. AE usually affects the liver; direct extension to (and destruction) of contiguous tissues may occur, as may metastatic lesions.


A presumptive diagnosis can be based on a combination of the person’s exposure history and imaging studies, such as an ultrasound or CT scan. Lesions may be found incidentally in asymptomatic people. Serologic testing also may be helpful. Additional information and diagnostic assistance (serologic, parasitologic, and molecular) are available through CDC (; 404-718-4745;


For CE, WHO has developed an image-based staging system that facilitates selecting among potential case-management strategies, including observation without treatment, percutaneous approaches, surgical resection, and benzimidazole therapy (albendazole [drug of choice] or mebendazole). For AE, treatment strategies include complete surgical removal of infected tissue (if resectable) and long-term benzimidazole therapy; untreated AE progresses and ultimately leads to death.


Advise travelers to avoid contact with dogs and wild canids in endemic areas. Also advise travelers not to drink untreated water from streams, canals, lakes, or rivers, and to observe food and water precautions (see Chapter 2, Food & Water Precautions).

CDC website:


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Barbara L. Herwaldt, Susan Montgomery, Sharon L. Roy