Antibody Detection
The acute manifestations of human fascioliasis may precede the appearance of eggs in the stool by several weeks; immunodiagnostic tests may be useful for early indication of Fasciola infection as well as for confirmation of chronic fascioliasis when egg production is low or sporadic and for ruling out "pseudofascioliasis" associated with ingestion of parasite eggs in sheep or calves' liver.  The current tests of choice for immunodiagnosis of human Fasciola hepatica infection are enzyme immunoassays (EIA) with excretory-secretory (ES) antigens combined with confirmation of positives by immunoblot.  Specific antibodies to Fasciola may be detectable within 2 to 4 weeks after infection, which is 5 to 7 weeks before eggs appear in stool.  Sensitivity for the FAST-ELISA format of EIA was reported to be 95%, while sensitivity for the immunoblot using 12-, 17-, and 63-kDa antigens appeared to be 100%.  However, some cross-reactivity occurs in the FAST-ELISA with serum specimens of patients with schistosomiasis.  Antibody levels decrease to normal 6 to 12 months after chemotherapeutic cure and can be used to predict the success of therapy.

Reference:

Hillyer GV. Serological diagnosis of Fasciola hepatica. Parasitol al Dia 1993;17:130-6.