Anthelmintic activity in vitro of Citrus sinensis and Melaleuca quinquenervia essential oil from Cuba on Haemonchus contortus

Gastrointestinal nematodes are an important problem in the small ruminant production and their control nearly exclusively depends on commercial anthelmintics. However, parasite resistance to those chemical formulations is an increasing global problem, so new plant-derived compounds are being studied for their potential use against gastrointestinal nematodes. Citrus sinensis and Melaleuca quinquenervia essential oils were evaluated against Haemonchus contortus Embrapa2010 resistant isolate, through the egg hatch test (EHT) and larval development test (LDT) at concentrations ranging from 0.02 mg/mL to 50 mg/mL and from 0.04 mg/mL to 3.12 mg/mL, respectively. All concentrations, positive controls (thiabendazole in EHT or ivermectin in LDT), and negative controls (2% Tween 80 in EHT or 0.5% DMSO in LDT) were performed in six replicates and in three independent experiments, for a total of 18 repetitions involving approximately 1800 parasites per treatment. Significant differences (P <= 0.01) of inhibition percentages were identified by one-way analysis of variance followed by the Tukey test. Inhibitory concentration values (IC50 and IC90) were analyzed by the Probit procedure of SAS. The essential oils evaluated showed that C. sinensis presented limonene as major component (96.0%), while M. quinquenervia contained longifolene (32.95%) and 1,8-cineole (25.43%) as major components. In the EHT, the IC50 and IC90 of the essential oils were respectively 0.27 and 0.99 mg/mL for C. sinensis and, 1.52 and 5.63 mg/mL for M. quinquenervia. In the LDT, the IC50 and IC90 were 0.97 and 2.32 mg/mL for C. sinensis and, 0.44 and 0.94 mg/mL for M. quinquenervia. C. sinensis was five times more effective on eggs than M. quinquenervia. However, it was twice more effective on larvae than C sinensis, indicating that bioactive essential oils have different modes of action. The results suggest that these compounds are good candidates for nematode control. However, alternative anthelmintics have to be safe to the host, promote parasite control in vivo and not generate residues. So, all these key points need to be elucidated before using any plant extract and/or components. (C) 2015 Published by Elsevier B.V.