Increasing reports of anthelmintic resistance of the liver fluke Fasciola hepatica pose a threat to sheep farming in many countries worldwide. Particularly resistance to triclabendazole, the only flukicide effective against the highly pathogenic juvenile flukes, is of major concern. However, data about the susceptibility of F. hepatica to flukicides in Germany were lacking. Therefore, a field study was conducted from 2020-2022 to evaluate the frequency of F. hepatica on German sheep farms and to test the efficacy of triclabendazole and albendazole by means of a Faecal Egg Count Reduction Test (FECRT) and a Coproantigen Reduction Test (CRT). In advance of the field study, a systemic comparison between three coproscopical methods was conducted in order to determine the most appropriate method for the FECRT. Sufficient fasciolicidal efficacy of albendazole was proven on 1/1 farm and triclabendazole was efficient on 10/11 farms. One one farm, complete failure of triclabendazole, even in double the recommended dose, was observed associated with massive animal losses due to acute fasciolosis. This is the first report of triclabendazole resistance in Germany. The results indicate, that flukicide resistance is not widespread in Germany so far, but the observations clearly illustrate the drastic consequences of triclabendazole resistance. Due to the lack of alternative drugs to eliminate juvenile flukes, triclabendazole resistance should be considered a serious therapy emergency in sheep and resistance might spread in the future.
