Efficacy of Benzimidazole Anthelmintics Against Cattle Strongyles in Alba County: An In Vitro Study

Nematode infections in ruminants have medical and economic negative impacts. Parasitic infestations lead to major losses due to treatment and prevention costs, reduced weight gain, and compromised animal welfare. The majority of commonly used anthelmintics are from three chemical classes: benzimidazoles, macrocyclic lactones, and imidazothiazoles. The development of resistance against one compound often implies cross-resistance within the same class. The study aimed to evaluate the efficacy of four benzimidazoles against gastrointestinal strongyles: albendazole (ABZ), mebendazole (MBZ), thiabendazole (TBZ), and fenbendazole (FBZ). The study was conducted in vitro on a group of 41 cattle from Alba County. Two types of tests were performed: Egg Hatch Assay (EHA) and Larval Development Assay (LDA). The lowest lethal concentration 50 (LC50) was exhibited by FBZ (1.099 µg/ml), followed by ABZ (2.111 µg/ml) and MBZ (3.173 µg/ml). The minimum inhibitory concentration (MIC) highlighted the highest efficacy of MBZ (0.343 µg/ml), followed by FBZ (0.415 µg/ml). ABZ tests showed no significant differences between the LC50 and MIC values. EHA revealed strongyle resistance to ABZ, MBZ, and FBZ. LDA highlighted strongyle resistance to ABZ and sensitivity to MBZ and FBZ. FBZ had the lowest LC₅₀ and MIC concentrations. The highest resistance risk was found in ABZ.