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Objectives
To establish a protocol for IgG detection in urine specimen by enzyme-linked immunosorbent assays and assesses its value in diagnosis of strongyloidiasis in comparison with the conventional serum-based serodiagnosis and parasitological methods.
Methods
Indirect enzyme-linked immunosorbent assay method (ELISA) was developed to detect Strongyloides- specific IgG in urine and employed Receiver operating characteristic analysis (using MedCal vXXX) to obtain a cutoff point for serodiagnosis of strongyloidiasis. The conventional serum-based ELISA system was also performed to analyze the matched pair serum specimens originated from the same subjects.
The sample populations were drawn from villagers in Ban Phai, Munchakiri and Chonnabot districts in Khon Kaen Province. Serum, faeces and urine were collected from each individual subject and processed for diagnoses. Within the sample of 51 subjects, 42 (82.3%) were positive for strongyloidiasis based on agar plate culture (APCT) and formalin-ethyl acetate concentration techniques (FECT). Performances of urine and serum ELISA were evaluated using the parasitological methods as a reference.
Results and Discussion
The new urine ELISA for diagnosis of strongyloidiasis had the sensitivity and specificity of 78.5% and 22.2%, respectively and those for serum ELISA were 76.1% and 66.6%, respectively. The seroprevalence determined by urine ELISA (78.4%) was higher than that by serum ELISA (68.8%) but lower than the parasitological methods (80.4%). Comparable prevalences of strongyloidiasis were obtained when determined by urine ELISA and that by parasitological methods, hence suggested that the urine ELISA is more sensitive than serum ELISA. In particular, within Strongyloides-negative subjects (n=9), 7 cases (77.8%) were positive by the urine ELISA while only 3 cases (33.3%) were positive by the serum ELISA. In Strongyloides-positive subjects (n=41), the urine ELISA detected 33 positive cases (80.49%) which were similarly detected by the serum ELISA (32 cases, 78.05%). The urine ELISA showed no cross reaction with Opisthorchis viverrini (n=11), Taenia (n=3), Trichuris (n=1) and hookworms (n=13). In the serum ELISA, no cross reaction was found in Angiostrongylus cantonensis (n=2), Taenia (n=1) and hookworms (n=2). However, considerable cross reactions occurred with Ascaris lumbricoides and Echinostomes which are relatively rare in the study area.
Conclusion
The established protocol for urine ELISA in serodiagnosis of strongyloidiasis showed similar sensitivity to serum ELISA and is also comparable to the standard APCT. In particular, the urine IgG ELISA is more sensitive in faecal negative cases. Since collection of urine is non invasive, the urine ELISA has potential applicability for diagnosis as well as mass screening of strongyloidiasis prior to a standard confirmatory test
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