Echinococcus Species - Echinococcosis Infection

Echinococcosis is an infection caused by tapeworms in the Echinococcus genus and occurs when humans accidentally ingest tapeworm eggs, usually as a result of contact with an infected animal or its stool.   Symptoms emerge from cyst- or vesicle-like larvae growing in different organs of the body.    Because the cysts and vesicles grow slowly, symptoms may not appear until years after initial ingestion.   

Most cases of echinococcosis are caused by E. granulosus (which leads to cystic echinococcosis).  E. granulosus is not endemic to the United States, and most infections are diagnosed in individuals who have emigrated from endemic areas.  Cysts are usually located in the liver or lungs, and symptoms include abdominal pain, nausea, and vomiting.  Alveolar echinococcosis may be found worldwide but is rare in humans. 

Echinococcosis is mainly diagnosed by imaging techniques supported by serologic testing.  If serology is uninformative, fine needle biopsy may help confirm the diagnosis. 

Quick Answers for Clinicians

Which epidemiologic factors may indicate assessment for echinococcosis?

Echinococcus granulosus, the parasite that causes cystic echinococcosis, is very rare in North America and is more often found in Africa, Europe, Asia, the Middle East, and Central and South America.  Livestock, especially sheep, serve as an intermediate host for E. granulosus.  Human infection is more common in individuals involved in raising sheep, especially when dogs live in close contact with people, when the slaughter of livestock is uncontrolled, and in unsanitary conditions.   In these conditions, dogs, which are definitive hosts, may consume infected organs from sheep carcasses. The feces of these dogs contain E. granulosus eggs and may contaminate soil, food, or water that is then unintentionally consumed by humans, resulting in infection. 

Which imaging techniques are useful in the diagnosis of echinococcosis?

Computed tomography (CT) scans, magnetic resonance imaging (MRI), and ultrasound imaging may be used to detect and evaluate fluid-filled cysts caused by cystic echinococcosis, and radiography may be used to detect either calcified cysts or fluid-filled cysts in the lungs. 

Indications for Testing

Laboratory testing for echinococcosis should be performed when cyst-like masses are identified via imaging in an individual with suggestive symptoms (eg, abdominal pain) and a history of exposure to host animals in an endemic region.

Laboratory Testing

Serology

The detection of Echinococcus antibodies (immunoglobulin G [IgG]) is supportive of a diagnosis of echinococcosis.  Seroconversion between acute and convalescent samples provides strong evidence of infection; testing on both should be performed at the same laboratory and at the same time.

A negative result does not rule out echinococcosis, however, because some infected individuals do not have detectable antibodies due to the location, vitality, and integrity of the cyst(s).  Additionally, false-positive results may occur in the presence of other disorders (eg, liver cirrhosis and cancer) or due to cross-reactivity with other antibodies (eg, cysticercosis antibodies).  As such, results should be interpreted in the context of patient history and other clinical findings. 

An enzyme-linked immunosorbent assay (ELISA) kit is available commercially in the U.S. for the detection of, but not the differentiation between, antibodies against E. granulosus (which causes cystic echinococcosis) and E. multilocularis (which causes alveolar echinococcosis).   There are no commercial tests in the U.S. that can differentiate between infection caused by E. granulosus and infection caused by E. multilocularis. 

ARUP Laboratory Tests

References

Medical Experts

Contributor

Jackson

Brian R. Jackson, MD, MS
Associate Professor of Pathology (Clinical); Adjunct Associate Professor, Biomedical Informatics, University of Utah
Medical Director, Support Services, IT, and Business Development, ARUP Laboratories