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Echinococcus Species - Echinococcosis Infection

Last Literature Review: October 2024 Last Update:

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Brian R. Jackson, MD, MS
Brian R. Jackson, MD, MS
Adjunct Professor of Pathology and Biomedical Informatics, University of Utah
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Echinococcosis, an infection caused by tapeworms in the Echinococcus genus, occurs when humans accidentally ingest tapeworm eggs, usually following contact with an infected animal (ie, a dog or other canid) or its stool. Symptoms emerge over an extended period of time as cyst- or vesicle-like larvae slowly grow in various organs of the body (eg, liver, lungs, etc.). 

Cystic echinococcosis (CE) and alveolar echinococcosis (AE) are the most typical forms of the disease, caused by E. granulosus and E. multilocularis, respectively.  Neotropical echinococcosis (NE), caused by E. vogeli and E. oligarthrus, is very rare,  and laboratory testing for the disease has not been sufficiently studied.  The majority of CE, AE, and NE cases are imported into the United States, although local cases of CE and AE have been reported.  In individuals with suspected echinococcosis, a presumptive diagnosis can be made with imaging and a thorough patient history. ,  Serology can then be used to support a diagnosis. If serology is uninformative, a fine needle biopsy may help confirm the diagnosis.  Molecular or histopathologic demonstrations of E. granulosus or E. multilocularis provide definitive evidence of CE or AE, respectively. 

Quick Answers for Clinicians

Which epidemiologic factors may indicate assessment for echinococcosis?

Within the life cycle of Echinococcus species, humans are unintended hosts. Human infection typically occurs in rural settings following contact with the feces of wild or domesticated canids (definitive hosts) carrying the disease. These canids become infected through the consumption of intermediate hosts, including sheep, swine, goats, cattle, camels, deer, and various rodents. E. granulosus (causative of cystic echinococcosis, the most frequent form of the disease) is broadly distributed across the globe, whereas E. multilocularis (causative of alveolar echinococcosis) is found in the Northern Hemisphere. E. vogeli and E. oligarthrus, which cause the rarer neotropical echinococcosis, are limited to Central and South America. , 

Indications for Testing

Laboratory testing for echinococcosis should be performed in symptomatic patients with a compatible exposure history when cyst-like masses or tumor-like lesions are identified via imaging. Signs and symptoms may include right epigastric pain, abdominal pain, nausea, vomiting, hepatic enlargement, chronic cough, and biliary obstruction. ,  Testing may also be considered in asymptomatic individuals with increased risk based on epidemiologic factors. 

Laboratory Testing

Diagnosis of CE and AE involves a combination of imaging and serology, interpreted in the context of clinical findings and patient history.  Enzyme immunoassays (EIAs) are preferred for initial laboratory testing. Due to limitations in test specificity, positive or equivocal results should be confirmed by immunoblot. , ,  Some of these tests may only be available through public health laboratories such as the CDC.

Serology for echinococcosis is subject to cross-reactivity in the presence of certain helminth infections (eg, Taenia solium), malignancies, cirrhosis, and P1 antibodies. ,  Currently, there are no commercial assays available in the United States that can differentiate between E. granulosus and E. multilocularis infection. 

If serology is uninformative, fine needle biopsy may help confirm a diagnosis, although this approach carries a risk of allergic reaction (ie, to hydatid fluid leakage) and secondary recurrence.  Resected specimens may also be tested. Molecular or histopathologic demonstration of E. granulosus or E. multilocularis provides definitive evidence of CE or AE, respectively. 

Cystic Echinococcosis

To identify CE, enzyme-linked immunosorbent assays (ELISAs), indirect hemagglutination (IHA) tests, indirect fluorescent antibody (IFA) tests, and latex agglutination tests (LATs) can be performed. , ,  Among these, ELISAs are the most commonly used test method.  Test performance varies by methodology and the materials (eg, antigen collected from various sources) used to manufacture the test. In addition, test sensitivity may also be impacted by patient immune status, the stage and site of cyst development, cyst viability (inactive cysts may produce negative results), and the integrity of the cyst wall, which confines any echinococcal antigens and in turn limits a patient’s immune response.  As such, a negative test result does not rule out the possibility of echinococcosis. , 

Notably, although CE relapse occurs frequently, and persistently elevated titers may suggest disease recurrence or residual infection, positive serologic results are possible even after the successful resection of a cyst. 

Alveolar Echinococcosis

Antibodies against E. multilocularis are measurable in a majority of patients with AE and can be detected by EIAs using purified, in vitro-produced, or recombinant E. multilocularis antigens. ,  Sensitivity and specificity are improved in serologic tests that use two purified E. multilocularis antigens, although such tests are not currently available in the United States. 

Following diagnosis, regular treatment monitoring is recommended.  An ELISA that uses Em18 antigen can be used to determine treatment efficacy, whereas a test that uses Em2 antigen is preferred for postoperative assessment. 

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References

  1. 26677245

    Agudelo Higuita NI, Brunetti E, McCloskey C. Cystic echinococcosis. J Clin Microbiol. 2016;54(3):518-523.