Immunodetection of Fasciola gigantica Circulating Antigen in Sera of Infected Individuals for Laboratory Diagnosis of Human Fascioliasis

Abstract

ABSTRACTCurrently, the laboratory diagnosis of human fascioliasis is based on the parasitological examination of parasite eggs in stool specimens and serological detection of specific antibodies in serum samples, which are often unreliable diagnostic approaches. Ideally, a sensitive and specific diagnostic test forFasciolainfection should be based on the detection of circulatingFasciolaantigen, which implies active infection. Here, a 27-kDa-molecular-mass antigen was identified in aFasciola giganticaadult worm antigen preparation, excretory-secretory products, and sera fromF. gigantica-infected individuals, and it was not detected in antigenic extracts of other parasites and sera from noninfected individuals. The target antigen was isolated and partially characterized as a protein. Immunoperoxidase staining located the target epitope within teguments and guts ofF. giganticaadult worms. The performance characteristics of a newly developed enzyme-linked immunosorbent assay (ELISA) based onF. giganticacirculating antigen detection in serum (FgCA-27 ELISA) were investigated using sera of 120 parasitologically diagnosedF. gigantica-infected individuals and 80 noninfected individuals. The area under the receiving operating characteristic (ROC) curve (AUC) for ELISA was significantly high (AUC = 0.961,P< 0.0001) for discriminatingFasciola-infected and noninfected individuals. The developed assay showed high degrees of sensitivity, specificity, and efficiency (>93%), and a significant correlation (r= 0.715,P< 0.0001) between antigen level and parasite egg count was shown. In conclusion, a 27-kDaFasciolaantigen was identified in sera ofF. gigantica-infected individuals. A highly sensitive and specificFasciolaantigen detection assay, FgCA-27 ELISA, was developed for laboratory diagnosis of human fascioliasis.