Evaluation of the serodiagnostic potential of tegumental antigens in human fascioliasis

Abstract

Background:Fascioliasis was recognized as a serious public health problem in human with an estimated 17 million people infected worldwide.Enzyme Linked Immunosorbent Assay (ELISA) is considered the most sensitive and specific as an adjuvant to faecal analysis. Specificity of ELISA depended mainly on the degree of specificity and purity of the used antigen as well as history of the tested sera.Most of the immunodiagnostic assays of human fascioliasis rely on antibody detection using crude worm antigens of which the Somatic (S) and Excretory-secretory (E-S) ones constitute a major component.Also Tegumental proteins are an important source of immunodiagnostic antigens. Several F. giganticaantigens have been purified toenhance the specificity of the diagnostic assays from whichF. giganticaTAg from which the 16.5 KDasubunit was highlighted for further investigation. The different immunodiagnostic response between the different antigens and their fractions was an urge for us to study some of their responses comparatively in a simple, ELISA technique. Objective: The present study aims to comparatively evaluate the diagnostic performance of TAg and its 16.5 KDa subunitprepared from F. gigantica adult fluke to S and E-S Ags,in a standard total indirect IgG home-made conventional ELISA for serological evaluation of human fascioliasis. Study design: For serving this study, F. gigantica worms were collected from bile ducts of naturally infected cattle from a local abattoir at Cairo, Egypt,then Ags were prepared; S, E-S, T Ag and 16.5 KDategumental subunit (by fractionation of tegumental antigen through SDS-PAGE then elution from the gel). These Ags were introduced to an indirect TIgG ELISA. Three groups of patients were involved, Group I (15 fascioliasis patients), Group II (patients with other parasitic infections and negative for fascioliasis (8 cases of hydatidosis, 7 cases of intestinal schistosomiasis, 3 cases of amoebiasis and 2 cases of toxoplasmosis) and Group III (normal control group), it included 15 healthy individuals, confirmed to be negative for fascioliasis and the above mentioned parasitic diseases, then the results were statistically evaluated. Results: inTIgG-ELISA, the highest sensitivity calculated from ROC test was obtained by the T Ag (100%) followed by S Ag (86.6%) followed by E-S (73.3%) and least value was obtained from 16.5 KDa subunit (53.3%). As for the specificity, the highest value was obtained from T Ag (100%) followed by E-S Ag (79.2%) then the 16.5 KDa subunit (75%), and least value was obtained from S Ag (70.8%).The highest AUC value (1.0) was that of T Ag which was used as a reference value for the rest of the results. There was a significant outcome between the AUC values of T Ag compared to S and E-S Ags. While a highly significant outcome was found when compared to the 16.5 KDa T subunit.The dot diagram revealed that T Ag has the highest sensitivity and specificity. Conclusions: The studyhighlighted the potential of F. giganticaT Ag overS, E-Sand the 16.5 KDa T subunit in diagnosis of human fascioliasis, it seems to remain the most promising antigen as regards: sensitivity, specificity and diagnostic accuracy in conventional TIgG ELISA. This performance was followed by S and E-SAgs which showed nearly equivocal results. Unexpectedly, there was a poor diagnostic outcome from our selected 16.5 KDa T subunit. Keywords: Fascioliasis, F.gigantica, ELISA, Tegumental antigen, 16.5 KDa subunit,Somatic antigen, Excretory-secretory antigen.