We standardized and evaluated an ELISA technique for the detection of total and specific anti-Giardia duodenalis secretory IgA antibodies (slgA). Samples of saliva and serum of 161 Venezuelan schoolchildren were analysed. After stool examination, 66 children were diagnosed to be infected with Giardia duodenalis, 22 with other protozoa, and 73 non-parasitized. The mean (+ 2 SD) values of secretory IgA in the non-parasitized group was considered as the criterion of positivity. The levels of total and specific anti-Giardia slgA were significantly higher in children with Giardia compared with the group with other protozoa (p < 0.01) and the non-parasitized group (p < 0.001). The ELISA technique developed showed values of sensitivity and specificity of 74 and 94 per cent, respectively, a predictive value of 92 per cent for positive samples and 80 per cent for negative samples. Specific anti-Giardia IgA serum levels showed a low sensitivity (57 per cent) and a predictive value for negative samples (53 per cent). Our results suggest that secretory anti-Giardia IgA levels measured in saliva samples may reflect local intestinal IgA responses elicited by these parasites. Thus, determinations of the levels of slgA anti-Giardia could be a useful diagnostic tool for giardiasis in children.
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