Identification and characterization of a 26- to 28-kDa circulating antigen of Fasciola gigantica

As a disease of domestic ruminants, fascioliasis is of considerable economic importance. Although serological tests are available for the diagnosis of the disease, they are of generally low specificity because of cross-reactivity with antigens from other parasites. There is a need to identify other Fasciola antigens on which more specific tests could be based. In the present study, a specific rabbit anti-serum and western-blot analyses were used to demonstrate the presence of a highly reactive antigen of 26-28 kDa not only in an extract of adult F. gigantica but also in the excretory/secretury products of the worms and in the bile secretions and sera of cattle that were naturally infected with this parasite. The 26- to 28-kDa antigen was isolated from preparative polyacrylamide gels, by electro-elution. The purified antigen showed a single peak at 5.8 min when analysed by capillary zone electrophoresis. It was characterized as protein containing 47.5% hydrophilic and 29.3% hydrophobic amino acids. Immunostaining demonstrated that the target epitope was located in the gut and tegument of adult F. gigantica and within the bile ducts, the portal tracts of the livers and the mucosa and muscularis of the gallbladders of infected cattle. A simple and rapid dot-ELISA technique based on the specific rabbit anti-serum was 100% specific when tested on the sera from nine cattle infected with F. gigantea and 27 uninfected cattle. In conclusion, the 26- to 28-kDa Fasciola antigen may be a promising candidate for the immunodiagnosis of fascioliasis.