SEROPREVALENCE OF FASCIOLA-HEPATICA INFECTION IN SHEEP IN NORTHWESTERN SPAIN

To estimate the prevalence of Fasciola hepatica infection in sheep in the Leon province (northwestern Spain), we conducted a survey between October 1992 and May 1993. A total of 767 samples of feces and serum w ere collected from sheep over 1 year of age belonging to 152 flocks ra ndomly selected from the 4 natural regions of Leon province. Samples w ere analyzed by a standard coprological sedimentation method and an in direct enzyme-linked immunosorbent assay (ELISA) using excretory-secre tory products from F. hepatica as the antigen. The results showed the feasibility of using the indirect ELISA to facilitate the serodiagnosi s of ovine fasciolosis in seroepidemiology studies (95% sensitivity an d >99% specificity). No serological cross-reaction with infection by t he trematode Dicrocoelium dendriticum was found. Furthermore, a statis tically significant association was demonstrated between the mean floc k prevalence results as determined by ELISA (77.6%) and by coprologica l examination (23.7%; P<0.001). Differences in the results obtained by the two diagnostic methods could have been due to fluctuations in the numbers of fluke eggs detected in feces and to the persistence of spe cific antibodies in serum after an efficacious fasciolicide treatment. The median number of F. hepatica eggs detected per gram of feces was 10 (range, 5-450 eggs/g feces). The geographical distribution of F. he patica infection in Leon province was similar in all natural regions, probably due to the observation that meteorological conditions are not limiting for the maintenance of the parasite life cycle in any area o f the province and to the abundance of irrigated areas together with t he lack of planned control strategies. No significant association betw een trematode infection and sheep breed, flock size, or number of trea tments was found, but the results showed a significant association bet ween infection and untreated sheep (P<0.05).