Comparison of enzyme-linked immunosorbent assay and indirect immunofluorescence assay in the diagnosis of human strongyloidiasis.

BACKGROUND: An enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay (IFA) were evaluated for serological diagnosis of human strongyloidiasis. METHODS: Serum specimens obtained from 46 individuals infected with Strongyloides stercoralis, 37 healthy persons and 381 persons with other parasitic infections were tested using an IgG-ELISA that used crude antigen of S. stercoralis filariform larvae and an IFA. Test sera were pre-incubated with antigens from Ascaris, Toxocara and hydatid protoscolices to remove non-specific antibodies. RESULTS: The sensitivity, specificity, positive predictive value and negative predictive value for ELISA were 93.5%, 96.1%, 72.9% and 99.2%, respectively, and those for IFA were 87%, 90.1%, 49.4% and 98.4%, respectively. Both assays showed false positivity in hydatidosis, ascariasis and toxocariasis; however, this was less common with ELISA. CONCLUSION: ELISA method using filariform larval antigen may be a sensitive and specific test for human strongyloidiasis, and may be preferable to IFA.

Evaluation of the stability of coated plates with antigen at different temperatures and times by ELISA test to diagnose fasciolosis.

BACKGROUND: Considering that ELISA method presently is the test of choice for diagnosis of fasciolosis, the present study was undertaken to evaluate the maximum validity of coated plates at different temperatures and different times during one year of evaluation. METHODS: Serum samples of patients infected with fasciolosis (n=10), hydatidosis (n=5), toxocariasis (n=5), and negative control sera (n=5) were examined. Two series of plates were considered. The first series were coated with Fasciola homogenate Ag 12 ug/ml, and after some steps were blocked with gelatin and preserved at different temperatures as -80°C, -20°C, -4°C and +4°C. The 2(nd) series were treated under the same criteria but were not blocked with gelatin. Each series were examined by ELISA test from 1(st) month to 12(th) month. Sera with 1:125 dilution, and peroxidase-conjugated goat anti-human IgG diluted 1:10000 were considered optimum. RESULTS: To ease reporting the results and due to many similarities only results related to 1(st), 6(th) and 12(th) months were analyzed and sensitivity, specificity plus cut-off were determined for each series separately. CONCLUSION: Preserving the coated plates, while unblocked at -80°C for 6-8 months is pertinent and functional and in that case, we can be sure the best out put would be applicable.