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Dicrocoeliosis is a parasitic disease caused by trematodes belonging to the genus Dicrocoelium. These small liver flukes are found in the bile ducts of the definitive host (ruminants, but also equids, lagomorphs, humans), and usually produce no symptoms; only in massive infections can dicrocoeliosis be diagnosed clinically. For this reason dicrocoeliosis often remains undetected and its diagnosis is mostly based on post-mortem examination of the liver or on coprological assays for in vivo diagnosis. However, the latter method has scant sensitivity and because of the long prepatency of Dicrocoelium spp. only permits late diagnosis. In the present study, an Enzyme Linked Immunosorbent Assay (ELISA) technique is developed as a potential tool for early serological diagnosis, with higher sensitivity and specificity than current diagnostic techniques. Antigen used in the ELISA test was prepared from excretory/secretory and somatic products of D. dendriticum. Serum samples from experimentally infected lambs and from the field were investigated using the test. The ELISA test detected antibodies from day 30 post infection, whereas coprological samples were only positive two months post infection. Cross-reactions with other helminths were tested; the test lacked specificity when using somatic antigen, and some cross reactions were detected in animals naturally infected by Fasciola hepatica. The antigens obtained were also processed by electrophoresis on poliacrylamide gel sheets and an immunoblot analysis was performed in order to characterise the protein fractions and their antigenic role in sera of infected sheep. In a field test 892 sera from sheep of Trentino Province (northeastern Italy) were screened by the ELISA test for dicrocoeliosis. A high proportion of positives were found, from 80 to 100%; this is in accordance with previous surveys carried out in Italy. It is concluded that indirect ELISA is a useful method for the diagnosis of dicrocoeliosis in sheep, especially for sero-epidemiological surveys.