The sensitivity and specificity of ELISA in human strongyloidiasis have been evaluated using lyophilized larval antigen suspended in PBS (7.2). Study included 78 patients proven to have Strongyloides stercoralis infection, 26 normal individuals and 42 patients with different endemic parasitic infections.
Sensitivity was 79.5% and specificity was 98.5%. No cross reaction between S. ster coralis antigen and Schistosoma mansoni, Fasciola hepatica. Entamoeba histolytica Ascaris lumbricoides. Oxyuris and Hymenolepis nana was detected. One of eight cases with Giardia lamblia infection showed cross reaction.
INTRODUCTION
S. stercoralis is a soil transmitted intestinal nematode parasite which is primarily adapted to warm climates (1). In the great majority of cases S. stercolaris infection is benign being discovered as an incidental finding (2). Carosi et aL (3) found that out of 50 patients studied, 34% had acute enteritis, 22% had chronic enteritis, 22% had cutaneous allergy and 22% were asymptomatic. Serological tests are important aids in detecting cases of hidden or light infection, such as: precipitin test, filarial comple ment fixation test, indirect haemagglutination test, indirect immunofluorescent anti body test and enzyme-linked immunosorbent assay (ELISA). The main goal of this study was to prepare S. stercoralis antigen pure enough to be sensitive and specific in serodiagnosis of the infection and to minimise the chance of cross reaction with other endemic parasites.
MATERIAL AND METHODS
This study was performed on 78 patients proven to have S. stercoralis, 26 normal individuals and 42 patients with different endemic parasitic infections. Antigen was prepared from cultured S. stercoralis rhabditiform larvae. Larvae were washed repeat ediv in PBS (pH. 7.2) and destructed by sonication. The suspension was centrifuged at 20.000 rpm at 4°C for one hour. Supernatant was dialyzed overnight against PBS. Dialysate was lyophilized, then reconstituted in known volume of PBS 7.2. Protein content was determined by lowery method (4).
Serological diagnosis was attempted by ELISA. Optimal antigen concentration used for coating 96 wells of flat bottom polystyrene plate was 5 Mg/MI in 0.1 molar carbonate buffer, ph 9.6 (coating buffer) at room temperature (50 uI/well).
Blocking was done with 0.1% Bovine serum albumin in coating buffer for one hour at room temperature (100 uI/well).
Optimal serum dilution (1/40) in phosphate buffered saline containing 0.05% Tween 20 (PBS.T) was put in the plate wells (50 uI/well) for 2 hours in a shaking wa ter bath at 37 C. Coat antihuman IgG alkaline phosphatase labelled (Sigma) 1:1000 di EMJ Vol.7 No.9 Sept., 1990 (503)
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