Echinococcosis

Infectious Agent

Larval stages of taeniid cestodes of the genus Echinococcus .

Transmission

Oral contact with contaminated dog feces, particularly in the course of playful and close contact between children and dogs, or through contaminated food or water.

Epidemiology

Echinococcus granulosus is prevalent in broad regions of Eurasia, several South American countries, North and Central America, and Africa. Foci of transmission are found in many other countries. In nonendemic countries, E. granulosus is typically seen among immigrants or refugees coming from endemic countries. E. multilocularis is endemic in the central part of Europe, parts of the Near East, Russia, the Central Asian Republics, China, northern Japan, northwestern Canada, and Alaska. E. vogeli is indigenous to the humid tropical forests in central and northern South America. A small number of polycystic echinococcosis cases in these areas are caused by E. oligarthrus .

Clinical Presentation

Cystic Echinococcosis or Cystic Hydatid Disease

In humans, hydatid cysts of E. granulosus are slowly enlarging masses comparable to benign neoplasms; most human infections remain asymptomatic. Clinical manifestations are determined by the site, size, and condition of the cysts. Hydatid cysts in the liver and the lungs together account for 90% of affected localizations.

Alveolar Echinococcosis or Alveolar Hydatid Disease

The embryo of E. multilocularis seems to localize invariably in the liver of the intermediate host (such as wild rodents) and humans. Patients eventually die from hepatic failure, invasion of contiguous structures, or less frequently, metastases to the brain.

Polycystic Echinococcosis or Polycystic Hydatid Disease

Polycystic echinococcosis is usually caused by E. vogeli or E. oligarthrus . Relatively large cysts develop over years and are primarily found in the liver and occasionally in the thorax or abdominal cavity. Those who are symptomatic may present with a painful right hypochondrial mass, progressive jaundice, or, as in the other forms of disease, liver abscess(es).

Diagnosis

A presumptive diagnosis can be made on the basis of a combination of the individual’s history and imaging studies, such as an ultrasound or CT scan. Lesions may be found incidentally in an asymptomatic person. Serologic assays may also be performed, and newer ones are under development. Additional information and diagnostic assistance are available through CDC (www.cdc.gov/dpdx; 404-718-4745; parasites@cdc.gov).

Treatment

For cystic echinococcosis, treatment depends on cyst characteristics and cyst type. WHO has developed ultrasound criteria than can assist in determining treatment strategies. Some uncomplicated cysts do not require any treatment. Surgical removal is preferred when cysts are large (>10 cm), secondarily infected, or located in certain organs (brain, lung, or kidney). PAIR (puncture, aspiration, injection, reaspiration) is a minimally invasive technique used to treat some types of cysts in the liver and other abdominal locations. It is less risky and less expensive than surgery. Benzimidazoles (albendazole, mebendazole) should be given to prevent recurrence after surgery or PAIR. Additional percutaneous interventions are sometimes needed. Benzimidazoles may be used to treat small cysts (<5 cm). Albendazole should be given continuously, with no monthly treatment interruptions and in 2 divided doses, with a fat-rich meal to increase its bioavailability. Approximately 30% of patients treated with albendazole are cured after 3–6 months, and even higher proportions (30%–50%) demonstrate regression of cyst size and alleviation of symptoms.

Alveolar hydatid disease may require surgery and long-term albendazole but has a high case-fatality ratio. Praziquantel is used in some circumstances. Management of complex cases may require consultation with a tropical medicine specialist.

Prevention

Advise travelers to avoid contact with dogs or wild canids in endemic areas. Also advise them 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: www.cdc.gov/parasites/echinococcosis

Bibliography

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Authors

Pedro L. Moro, Paul T. Cantey