Author(s): Paul Cantey, Rebecca Chancey, Sharon Roy

Infectious Agents

Echinococcosis is caused by cestode parasites of the genus Echinococcus, including E. multilocularis, E. granulosus, and others.

Transmission

Humans become infected through ingestion of Echinococcus eggs shed in the feces of infected definitive hosts, including foxes and other canids for E. multilocularis, or dogs and other canids for E. granulosus. Ingestion can occur through hand-to-mouth transfer of eggs or by consuming fecally contaminated food, water, or soil.

Epidemiology

The 2 main forms of echinococcosis in humans are alveolar echinococcosis (AE), caused by E. multilocularis, and cystic echinococcosis (CE), caused by E. granulosus and other species. Rarer forms, referred to as neotropical echinococcosis (NE), are caused by E. vogeli and E. oligarthrus. AE occurs in the northern hemisphere, in parts of North America and Eurasia. CE occurs in parts of Africa, the Americas (including South America [foci within Peru]), Australia, and Eurasia, including in pastoral and rangeland areas, where transmission often is maintained by dog-sheep-dog cycles. NE occurs in rural settlements near tropical forests in Central and South America. Although indigenous human cases of AE and CE have been reported in the United States, most US cases of echinococcosis have been imported.

Clinical Presentation

People with AE and CE could 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. AE usually affects the liver; direct extension to and destruction of contiguous tissues can occur, as can metastatic lesions. In CE, 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 can develop in other organ systems. NE is rare; the polycystic form can be clinically similar to AE.

Diagnosis

A presumptive diagnosis can be based on a combination of the person’s exposure history and imaging studies (e.g., an ultrasound or CT scan). Lesions might be found incidentally in asymptomatic people. Serologic testing also can be helpful and is available through the Parasitic Diseases Branch at the Centers for Disease Control and Prevention (CDC). Instructions on how to submit a serum specimen for testing can be found at www.cdc.gov/laboratory/specimen-submission/index.html. For assistance with parasitological diagnosis, submit a request to the Division of Parasitic Diseases and Malaria DPDx.

Treatment

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. For CE, the World Health Organization has developed an image-based staging system that facilitates selecting among potential case-management strategies, including observation without treatment, percutaneous approaches, surgical resection, and drug treatment. Treatment of NE might involve surgical treatment or benzimidazole therapy; the role of percutaneous treatment is unclear. Clinicians can consult CDC to obtain more information about diagnosis and treatment (CDC Parasitic Diseases Inquiries: 404-718-4745 or parasites@cdc.gov).

Prevention

To reduce the risk for echinococcosis, travelers should avoid contact with dogs and wild canids in endemic areas; should not drink untreated water from canals, lakes, rivers, or streams; and should follow food and water precautions (see Sec. 2, Ch. 8, Food & Water Precautions). In addition, travelers should practice good hand hygiene after handling dogs and during food preparation in affected areas.

CDC website: Echinococcosis