Serodiagnosis of giardiasis: identiflcation of immunoglobulin G anti-Giardia duodenalis in sera by ELlSA

Abstract

Diagnosis of Giardia duodenalis infections is based upon identification of cysts or trophozoites in fecal samples. However, sensitivity of parasitological methods reaches a maximum of 85% in multiple samples, due to intermittent excretion of cysts. Presence of antibodies does not distinguish between a recent or a past infection, but they can aid in differential diagnosis. The aim of this study was to standardize and evaluate an immunoenzymatic assay (ELISA) for the detection of anti-Giardia duodenalis IgG antibodies in sera from infected patients. Antigen was prepared from cultured trophozoites initially obtained from the small intestine of gerbils (Meriones unguiculatus) that had been previously infected with cysts purified from positive human fecal samples. Sixty sera from patients with parasitologically demonstrated Giardia infection (positive samples) and 47 sera from umbilical cords (negative samples) were used to standardize and evaluate the test. Anti human IgG linked to alkaline phosphatase was used as conjugate. The optimum concentration of G. duodenalis trophozoite antigen was 15 ug/ml and the optimum dilutions of sera and conjugate were 1 :25 and 1 :400, respectively The cut-off value (absorbance) was 0.300. The pararneters of the test were: sensitivity, 98.3% (95% confidence interval (95%Cl): 89.9%-99.9%); specificity, 95.7% (95% CI: 84.3%-99.3%); positive predictive value, 96.7% (95% CI: 87.6% - 99.4%), and negative predictive value: 97.8% (95% GI: 87.0%-99.9%). The ELlSA test will improve the diagnosis of giardiasis and will be useful for epidemiological studies of seroprevalence.