Diagnostic Potential of Target Giardia lamblia Specific Antigen for Detection of Human Giardiasis Using Coproantigen Sandwich ELISA

Giardiasis is endemic in all regions of the world. Giardia lamblia (G. lamblia) cysts are spread in Egypt via the fecal-oral route, through ingestion of the cyst with contaminated food or water. The symptoms of giardiasis vary from the asymptomatic passage of cysts to chronic diarrhea, malabsorption and weight loss. Although microscopy has the advantage of low cost and ability to simultaneously detect other gastrointestinal parasite, the limitation of this method is that G. lamblia cysts are small and similar to many pseudoparasites. This study aimed to verify the advantages and disadvantages of enzyme-linked immunoassaying versus microscopy for diagnosing G. lamblia in human. The 65 kDa glycoprotein Giardia specific antigen (GSA-65 kDa) is considered to be an antigen of interest. It is shared by cysts and trophozoites of G. Lamblia as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis and immunoblotting and very specific to this parasite. Sandwich ELISA was more sensitive (95.12%) than ordinary parasitological diagnosis (78.05% for direct smear or 85.36% for MIFC method). Also, the NPV of sandwich ELISA (95.12%) is higher than that of parasitlogical procedure (82.35% for direct smear or 87.5% for MIFC method). On the other hand, the specificity (92.85%) and PPV (92.85%) of sandwich ELISA is lesser than that of parasitological procedure (100% and 100%, respectively). Sandwich ELISA, using purified anti-GSA-65 kDa IgG pAb, is recommended as a diagnostic test for Giardia spp. diagnosis more than ordinary microscopy methods.