The resistance of Haemonchus contortus to synthetic anthelmintics is of increasing concern; and different strategies are being evaluated to improve parasite control. The present study investigated the in vitro effects of combinations of synthetic compounds and monoterpenes. Additionally, the chemical association of the best combinations and their impact on the ultrastructural and biophysical properties of H. contortus eggs was evaluated. We assessed the efficacy of the monoterpenes, carvacrol, thymol, r-carvone, s-carvone, citral, and p-cymene and the anthelmintics, albendazole and levamisole using the egg hatch test (EHT) and the larval migration inhibition test (LMIT), respectively. The minimum effective concentrations of the monoterpenes, according to the EHT (efficacy ranging from 4.4%–11.8%) and LMIT (efficacy ranging from 5.6%–7.4%), were used in combination with different concentrations of synthetic compounds, and the IC₅₀ and synergism rate (SR) were calculated. Fourier-transform infrared spectroscopy (FTIR) was used to analyze the chemical association between the best combinations as revealed by the in vitro tests (albendazole and levamisole with r-carvone or s-carvone). Atomic force microscopy (AFM) was used to assess the ultrastructural and biophysical properties of H. contortus eggs treated with the albendazole and r-carvone combination. Among the monoterpenes, the highest efficacies were exhibited by carvacrol (IC₅₀ = 185.9 μg/mL) and thymol (IC₅₀ = 187.0 μg/mL), according to the EHT, and s-carvone and carvacrol (IC₅₀ = 1526.0 and 1785.3 μg/mL, respectively), according to the LMIT. According to the EHT, albendazole showed a slight statistically significant synergism in combination with r-carvone (SR = 3.8) and s-carvone (SR = 3.0). According to the LMIT, among the monoterpenes, r-carvone (SR = 1.7) and s-carvone (SR = 1.7) showed an increase in efficacy with levamisole; however, this was not statistically significant. The FTIR spectra of albendazole and levamisole, in association with r-carvone and s-carvone, indicated the presence of chemical interactions between the synthetic and natural molecules, contributing to the possible synergistic effects of these associations. Eggs treated with albendazole and r-carvone showed an increase in roughness and a decrease in height, suggesting that the treatment induced damage to the egg surface and an overflow of its internal contents. Overall, the combination of albendazole with r-carvone and s-carvone was efficacious against H. contortus, demonstrating a chemical association between the compounds; the significant changes in the egg ultrastructure justify this efficacy.

Haemonchus contortus对合成驱虫药的抵抗力越来越受到关注。正在评估不同的策略以改善寄生虫控制。本研究调查了合成化合物和单萜组合的体外作用。此外，最佳组合的化学结合及其对H. contortus超微结构和生物物理特性的影响鸡蛋进行了评估。我们使用卵孵化试验 (EHT) 和幼虫迁移抑制试验 (LMIT) 评估了单萜、香芹酚、百里酚、r-香芹酮、s-香芹酮、柠檬醛和对伞花烃以及驱虫剂、阿苯达唑和左旋咪唑的功效，分别。根据 EHT（功效范围为 4.4%–11.8%）和 LMIT（功效范围为 5.6%–7.4%），单萜的最低有效浓度与不同浓度的合成化合物组合使用，IC ₅₀并计算增效率（SR）。傅里叶变换红外光谱 (FTIR) 用于分析体外实验揭示的最佳组合之间的化学关联。测试（阿苯达唑和左旋咪唑与 r-香芹酮或 s-香芹酮）。使用原子力显微镜 (AFM) 来评估用阿苯达唑和 r-香芹酮组合处理的扭曲变形虫卵的超微结构和生物物理特性。在单萜中，根据 EHT，香芹酚 (IC ₅₀ = 185.9 μg/mL) 和百里酚 (IC ₅₀ = 187.0 μg/mL) 以及 s-香芹酮和香芹酚 (IC ₅₀= 1526.0 和 1785.3 μg/mL，分别），根据 LMIT。根据 EHT，阿苯达唑与 r-香芹酮 (SR = 3.8) 和 s-香芹酮 (SR = 3.0) 组合显示出轻微的统计学显着协同作用。根据 LMIT，在单萜中，r-香芹酮 (SR = 1.7) 和 s-香芹酮 (SR = 1.7) 显示出与左旋咪唑的疗效增加；然而，这在统计上并不显着。阿苯达唑和左旋咪唑的 FTIR 光谱与 r-香芹酮和 s-香芹酮结合，表明合成分子和天然分子之间存在化学相互作用，有助于这些结合的可能协同效应。用阿苯达唑和 r-香芹酮处理的鸡蛋表现出粗糙度增加和高度降低，表明该处理导致了鸡蛋表面的损坏和其内部内容物的溢出。总体而言，阿苯达唑与 r-carvone 和 s-carvone 的组合对H. contortus，证明化合物之间的化学关联；鸡蛋超微结构的显着变化证明了这种功效。