Diagnostic Findings [Last Modified: ]
Echinococcosis
[Echinococcus granulosus] [Echinococcus multilocularis]
[Echinococcus oligarthrus][Echinococcus vogeli]
Causal Agent Life Cycle Geographic Distribution Clinical Features Laboratory Diagnosis Treatment

Antibody Detection
Immunodiagnostic tests can be very helpful in the diagnosis of echinococcal disease, and should be used before invasive methods.  However, the clinician must have some knowledge of the characteristics of the available tests and the patient and parasite factors associated with false results.  False-positive reactions may occur in persons with other helminthic infections, cancer, and chronic immune disorders.  Negative test results do not rule out echinococcosis because some cyst carriers do not have detectable antibodies.  Whether the patient has detectable antibodies depends on the physical location, integrity, and vitality of the larval cyst.  Cysts in the liver are more likely to elicit antibody response than cysts in the lungs, and, regardless of localization, antibody detection tests are least sensitive in patients with intact hyaline cysts.  Cysts in the lungs, brain, and spleen are associated with lowered serodiagnostic reactivity, whereas those in bone appear to more regularly stimulate detectable antibody.  Fissuration or rupture of a cyst is followed by an abrupt stimulation of antibodies.  A patient with senescent, calcified, or dead cysts is generally found to be seronegative.

Cystic echinococcal disease (Echinococcus granulosus).  Indirect hemagglutination (IHA), indirect fluorescent antibody (IFA) tests, and enzyme immunoassays (EIA) are sensitive tests for detecting antibodies in serum of patients with cystic disease; sensitivity rates vary from 60 to 90%, depending on the characteristics of the cases.  Crude hydatid cyst fluid is generally employed as antigen.  At present, the best available serologic diagnosis is obtained by using combinations of tests.  EIA or IHA is used to screen all specimens; a positive reaction is confirmed by immunoblot assay or any gel diffusion assay that demonstrates the echinococcal "Arc 5."  Although these confirmatory assays give false-positive reactions with sera of 5 to 25% of persons with neurocysticercosis, the clinical and epidemiological presentation of neurocysticercosis patients should be rarely confused with that of cystic echinococcosis.  A commercial EIA kit is available in the United States.

Antibody responses have also been monitored as a way of evaluating the results of treatment, but with mixed results.  Following successful radical surgery, antibody titers decline and sometimes disappear; titers rise again if secondary cysts develop.  Tests for Arc 5 or IgE antibodies appear to reflect antibody decline during the first 24 months postsurgery, whereas the IHA and other tests remain positive for at least 4 years.  Chemotherapy has not been followed by consistent declines in antibody titers.  Consequently, the usefulness of serology to monitor the course of disease is limited; imaging techniques provide a more accurate assessment of the patient's condition.

Alveolar echinococcal disease (Echinococcus multilocularis).  Most patients with alveolar disease have detectable antibodies in serologic tests using heterologous E. granulosus or homologous Echinococcus multilocularis antigens.  With crude Echinococcus antigens, nonspecific reactions create the same difficulties as described above, however, immunoaffinity-purified E. multilocularis antigens (Em2) used in EIA allow the detection of positive antibody reactions in more than 95% of alveolar cases.  Comparing serologic reactivity to Em2 antigen with that to antigens containing components of both E. multilocularis and E. granulosus permits discrimination of patients with alveolar from those with cystic disease.  Combining two purified E. multilocularis antigens (Em2 and recombinant antigen II/3-10) in a single immunoassay optimized sensitivity and specificity.  These antigens are sold in a commercial EIA kit in Europe, but not in the United States.  As in cystic echinococcosis, Em2 tests are more useful for postoperative follow-up than for monitoring the effectiveness of chemotherapy.

Reference:

Lightowlers MW, Gottstein B.  Echinococcosis/hydatidosis: antigens, immunological and molecular diagnosis.  In: Thompson RCA, Lymbery AJ, eds. Echinococcus and hydatid disease. Wallingford, UK: CAB International, 1995; 355-410.

 
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