Strongyloidiasis laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Laboratory Findings
Eosinophilia
Blood eosinophilia is generally present during the acute and chronic stages, but may be absent with dissemination.[1]
Stool Smaples
- The gold standard for the diagnosis of Strongyloides is serial stool examination.
- The diagnosis rests on the microscopic identification of larvae (rhabditiform and occasionally filariform) in the stool or duodenal fluid.
- Duodenal aspirate is more sensitive than stool examination, and duodenal biopsy may reveal parasites in the gastric crypts, in the duodenal glands, or eosinophilic infiltration in the lamina propria.
- Specialized stool exams include Baermann concentration, Horadi-Mori filter paper culture, quantitative acetate concentration technique, and nutrient agar plate cultures.
- The stool can be examined in wet mounts:
- Directly
- After concentration (formalin-ethyl acetate)
- After recovery of the larvae by the Baermann funnel technique
- After culture by the Harada-Mori filter paper technique
- After culturing in agar plates
- The duodenal fluid can be examined using techniques such as the Enterotest string or duodenal aspiration.
- In disseminated cases of strongyloidiasis, larvae can be detected in sputum by simple wet-mount in fluid from a bronchoalveolar lavage (BAL).
- Diagnostic characteristics: length 200 to 250 µm (up to 380 µm); buccal cavity short, and prominent genital primordium.
A: The prominent genital primordium in the mid-section of the larva (black arrow) is readily evident. Note also the Entamoeba coli cyst (white arrow) near the posterior end of the larva.
Antibody Detection
- Immunodiagnostic tests for strongyloidiasis are indicated when the infection is suspected and the organism cannot be demonstrated by duodenal aspiration, string tests, or by repeated examinations of stool.
- Antibody detection tests should use antigens derived from Strongyloides stercoralis filariform larvae for the highest sensitivity and specificity.
- Although indirect fluorescent antibody (IFA) and indirect hemagglutination (IHA) tests have been used, enzyme immunoassay (EIA) is currently recommended because of its greater sensitivity (90%).
- Immunocompromised persons with disseminated strongyloidiasis usually have detectable IgG antibodies despite their immunodepression.
- Cross-reactions in patients with filariasis and some other nematode infections can occur.
- Antibody test results cannot be used to differentiate between the past and current infection.
- A positive test warrants continuing efforts to establish a parasitological diagnosis followed by antihelminthic treatment.
- Serologic monitoring may be useful in the follow-up of immunocompetent treated patients: antibody levels decrease markedly within 6 months after successful chemotherapy. [2]