Beyond Suspicion: An Australian Case Study of Anthelmintic Resistance and Integrated Liver Fluke Control in Sheep

Abstract

Liver fluke control in sheep relies heavily on TCBZ because of its efficacy against immature and adult Fasciola hepatica . However, repeated use without diagnostic monitoring can select for TCBZ resistance, which may be difficult to distinguish from other causes of treatment failure. This case follows a producer in the Southern Tablelands of NSW, Australia, who suspects resistance after liver fluke eggs are detected following treatment. Fourty-five Merino wethers are allocated to TCBZ, albendazole (ABZ), and untreated control groups. Animals are individually identified and weighed, and treatments are administered using calibrated equipment. Individual faecal samples are collected before treatment and again 21 days later. Paired and unpaired faecal egg count reduction tests estimate TCBZ efficacy at 79%, supporting a diagnosis of resistance, whereas ABZ efficacy remains above 95%. Comparison with coproantigen ELISA results demonstrates the value and limitations of combining diagnostic methods. The case shows that confirming anthelmintic resistance requires rigorous study design and may involve collaboration between veterinarians, diagnostic laboratories, and specialist parasitologists. Long-term control should integrate evidence-based treatment with grazing management, infrastructure maintenance, and reduced access to snail habitats to lower infection pressure and preserve remaining flukicides.