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Title: Synergistic interaction of ten essential oils against Haemonchus contortus in vitro

Author
item KATIKI, L. - Instituto De Zootecnia
item BARBIERI, A. - Instituto De Zootecnia
item ARAUJO, R. - Grasp Industria E Comercio Ltda
item VERISSIMO, C. - Instituto De Zootecnia
item LOUVANDINI, H. - The Center Of Nuclear Energy In Agriculture
item Ferreira, Jorge

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2017
Publication Date: 6/6/2017
Citation: Katiki, L.M., Barbieri, A.M., Araujo, R.C., Verissimo, C.J., Louvandini, H., Ferreira, J.F. 2017. Synergistic interaction of ten essential oils against Haemonchus contortus in vitro. Veterinary Parasitology. 243(2017):47-51. doi: 10.1016/j.vetpar.2017.06.008.

Interpretive Summary: Multi-drug resistant worms of livestock are a worldwide problem. Among them, the barber-pole worm (Haemonchus contortus) is the most serious impediment for small ruminant systems, with no new drug candidates currently under development. Natural compounds from plants have demonstrated anti-parasitic activity against insects and internal worms that afflict livestock and can aid animals cope with worm infections. In this work, several major components of plant essential oils found in citrus peel, eucalyptus leaves, thyme, cinnamon bark, etc, and named carvacrol, carvone, cineole, linalool, limonene, and thymol, cinnamaldehyde, anethole, vanillin, and eugenol were evaluated individually or in mixtures of binary, ternary, and quaternary combinations for their lethal effect against the eggs (ovicidal effect) of the barber-pole worm. These eggs hatch inside small ruminants, are released through feces, and account for animal reinfection due to pasture contamination. The main objective of this study was to identify the most effective anti-worm components used alone or in combination. The essential oils were ranked by the lethal concentration that killed 50% of the nematode eggs (LC50), in the following order (in mg/mL): cinamaldehyde (0.018), anethole (0.070), carvone (0.085), carvacrol (0.11), thymol (0.13), linalool (0.29), vanillin (0.57), eugenol (0.57), cineole (4.74), and limonene (207.5). Quantification of synergistic, additive, and antagonistic ovicidal effects were calculated for binary, ternary, and quaternary combinations. The best ovicidal effect resulting from synergistic activity among 16 different combinations was for cinnamaldehyde + carvacrol (LC50 0.012 mg/mL) and anethole + carvone (LC50 0.013 mg/mL). These results indicate that these binary combinations can be a promising natural control of barber-pole worms in sheep and goats. Essential oil affordability can benefit small ruminant growers who no longer can rely on failing commercial worm killers.

Technical Abstract: Anthelmintic resistance in sheep gastrointestinal nematodes is a worldwide problem. Multi-drug resistant haemonchosis is the most serious impediment for small ruminant systems, and there are no new drug candidates currently under development. Molecules from natural sources have demonstrated anthelmintic activity against parasites. In this work, the monoterpenoids carvacrol, carvone, cineole, linalool, limonene, and thymol and the phenylpropanoids cinnamaldehyde, anethole, vanillin, and eugenol were assessed individually or in mixtures of ten binary, three ternary, and three quaternary combinations using the in vitro egg hatch assay with eggs of a multi-drug resistant strain of Haemonchus contortus. The main objective of this study was to identify the most effective interaction among essential oils with the greatest individual anthelmintic efficacy and to determine the most powerful combinations. The essential oils were ranked by their 50% lethal concentration (LC50) as follows (mg/mL): cinamaldehyde (0.018), anethole (0.070), carvone (0.085), carvacrol (0.11), thymol (0.13), linalool (0.29), vanillin (0.57), eugenol (0.57), cineole (4.74), and limonene (207.5). Quantification of synergism, additive effect, and antagonism were calculated for binary, ternary, and quaternary combinations. The best anthelmintic effect resulting from synergistic activity among 16 different combinations was for cinnamaldehyde:carvacrol (LC50 0.012 mg/mL) and anethole:carvone (LC50 0.013 mg/mL). These results indicate that these binary combinations would be promising to be tested in sheep infected with H. contortus.