detection of Giardia lamblia coproantigen as a sensitive immunodiagnostic method for human giardiasis

This study was designed to develop a sandwich ELISA for detection of G. Iambiia antigens in stool and sera of giardiasis patients as a better diagnostic alternative to routine parasitological methods. Anti-G. Iamblia antibodies were produced by immunization of rabbit with G. lamblia antigen obtained from cultured trophozoites. Raised antibodies were then employed in sandwich ELISA for detection of G. lamblia antigen in collected sera and stool samples. In this study sera and stool samples from 80 G. lamblia infected patients, 71 patients infected with other parasites [Entamoeba histolytica, Schistosoma mansoni and Fasciola hepatica] and 30 uninfected individuals were tested by sandwich-ELISA for detection of G. lamblia antigen. The sensitivity of coproantigen assay reached 98.8% for detection of Giardia antigens in stool and 87.5% for detection of Giardia antigen in sera of giardiasis patients. The specificity of the assay was 94.1% for stool samples and 91% for sera of negative controls and patients harboring other parasites collectively. A positive correlation between age of patients and the antigen levels in both sera and stool samples of G. lamblia infected patients was observed. The sensitivity of antigen detection assay was directly related to the intensity of infection. The positivity rate for detection of coproantigen in stool was compared to the number of cysts in stool. Patients passing < 8 cysts showed false negativity in stool samples [one patient] compared to 100% positivity in patients passing > 50 cysts of stool [79 patients]. Moreover, a positive correlation was found between coproantigen level in stool and number of cysts in stool of G. lamblia infected patients [r=0.887, p< 0.001]. In conclusion, our data demonstrated that the employment of rabbit anti-G. lamblia IgG antibodies in sandwich ELISA for the detection of G. lamblia coproantigen in stool provided a sensitive and specific tool for immunodiagnosis of G. lamblia infection