In vitro anthelmintic activity of the monoterpene linalool, alone and combined with the nematophagous fungus Duddingtonia flagrans, in the control of gastrointestinal nematodes in horses.

This study evaluated, in vitro, the anthelmintic activity of the monoterpene linalool, alone and in association with the fungus Duddingtonia flagrans, against gastrointestinal nematodes of horses. Nematodes from the superfamily Strongyloidea, obtained from naturally infected horses, were used. The ovicidal activity of linalool was evaluated using the Egg Hatch Test (EHT). The larvicidal activity was evaluated using the Larval Motility Inhibition Test (LMIT), in which infective larvae (L3) were assigned to experimental groups treated with linalool alone (0.15, 0.3, 0.6, 1.25, 2.5, 5, 10, 20, 40, and 80 mg/mL), D. flagrans conidia alone (100,000, 500,000, and 1,000,000 conidia), or the combination of both. In the EHT, linalool completely inhibited egg hatching (100%) at all concentrations of 0.25 mg/mL and above, with an LC₅₀ of 0.15 mg/mL (0.015%). In the LMIT, linalool completely inhibited larval motility (100%) at all concentrations of 0.5 mg/mL and above, with an LC₅₀ of 0.103 mg/mL (0.010%). The association with the fungus D. flagrans promoted a significant reduction (p ≤ 0.05) in the number of live larvae after 72 h, reaching 100% inhibition within 14 days. The groups treated only with conidia showed lower efficacy, whereas the association with linalool enhanced the antiparasitic effect without impairing trap formation or the predatory capacity of the fungus. Thus, the results demonstrated that linalool has relevant ovicidal and larvicidal activity, and that its association with D. flagrans constitutes a promising alternative for the biological control of helminth infections in horses.