Fasciola hepatica: Specificity of a coproantigen ELISA test for diagnosis of fasciolosis in faecal samples from cattle and sheep concurrently infected with gastrointestinal nematodes, coccidians and/or rumen flukes (paramphistomes), under field conditions.

Chronic fasciolosis is often diagnosed by faecal egg counting (FEC), following concentration of the eggs in the sample by a zinc sulphate floatation method. However, concentration by a sedimentation technique gives improved sensitivity. Interpretation of FEC results for fasciolosis is complicated by factors such as the long pre-patent period and irregular egg shedding. Thus, FEC reduction tests (FECRT), when used alone, are not completely reliable for diagnosis of anthelmintic susceptibility or resistance in local fluke populations, especially when parasite burdens are small. A Fasciola hepatica coproantigen ELISA test has been introduced which more accurately reflects the presence of flukes in the host bile ducts in late pre-patent infections, and absence of flukes following successful chemotherapeutic intervention. The aim of the present study was to elucidate the specificity of the F. hepatica coproantigen ELISA technique, particularly regarding potential cross-reactivity with rumen fluke (paramphistome), gastrointestinal nematode and coccidian infections. The method involved parallel testing of a large battery of faecal samples from field-infected cattle and sheep using floatation and sedimentation FECs and coproantigen analysis. No evidence was found for significant false positivity in the F. hepatica coproantigen ELISA due to paramphistome, coccidian and/or gastrointestinal nematode co-infections. With sedimentation FECs less than 10 F. hepatica eggs per gram (epg), the likelihood of a positive coproantigen result for the sample progressively decreased. Diagnosis of fasciolosis should be based on consideration of both FEC and coproantigen ELISA findings, to ensure optimum sensitivity for pre-patent and low-level infections.