Evaluation of the ovicidal activity of triclabendazole against eggs of Fasciola gigantica using the modified fasciola egg hatch assay

Fasciolosis is a cosmopolitan and economically significant zoonotic helminth disease affecting livestock and humans worldwide. Triclabendazole (TCBZ) is widely used for the treatment and control of fasciolosis; however, information regarding its ovicidal activity against the eggs of F. gigantica remains limited. The present study evaluated the ovicidal efficacy of TCBZ against the eggs of F. gigantica using a modified Fasciola Egg Hatch Assay (FEHA) that assessed both embryonic development and egg hatching. Eggs were exposed to different concentrations of TCBZ (1–2.5 µg/ml) for 24 h followed by drug removal, and under continuous exposure for 14 days. Embryonic development and hatchability of the eggs were assessed microscopically to determine the inhibitory effects of the drug on development and hatching. The results demonstrated that TCBZ inhibited embryogenesis and hatching of eggs in a concentration- and exposure-time-dependent manner. Following 24-hour exposure and subsequent drug removal, TCBZ produced partial inhibition of egg development and hatching, with comparatively lower ovicidal efficacy in the present experimental conditions. In contrast, continuous exposure of eggs to TCBZ for 14 days resulted in markedly greater inhibition, with almost complete suppression of hatching at 2 µg/ml (99.59%) and complete inhibition at 2.5 µg/ml (100%). Increasing concentrations of TCBZ progressively enhanced ovicidal efficacy and reduced egg hatchability, indicating strong antiparasitic activity against the egg stage of the parasite. These findings indicate that sustained exposure to TCBZ is essential for achieving maximum ovicidal activity against F. gigantica eggs and highlight the importance of both drug concentration and duration of exposure in determining the extent of embryonic inhibition.