Chemical profile and antiparasitic effects of Lippia origanoides essential oil against Rhipicephalus microplus, Haemonchus contortus, and Caenorhabditis elegans.

Growing antiparasitic resistance challenges parasite control in livestock, increasing interest in natural product-based alternatives for animal health and food quality. This study evaluated the in vitro activity of Lippia origanoides essential oil against Rhipicephalus microplus, Haemonchus contortus, and Caenorhabditis elegans. Fresh leaves of L. origanoides from Maranhão, Brazil, were used to obtain essential oil by hydrodistillation, and its chemical composition was determined by gas chromatography-mass spectrometry (GC-MS). Bioassays evaluated activity against R. microplus larvae (immersion and repellency), H. contortus eggs (hatch inhibition), and C. elegans adults (mortality), all using serial dilutions of essential oil. Experiments were performed in nine replicates, and results were analyzed by nonlinear regression. Chemical analysis of the oil revealed the main constituents: camphor (32.13%), β-bisabolene (10.02%) and camphene (6.66%). The larval immersion test of the oil showed an LC50 (letal concentration) of 7.48 mg/mL against ticks. A repellency assay revealed an RC50 (repellent concentration) of 0.058 mg/cm2 at 10 minutes. The egg hatch assay for H. contortus resulted in an LC50 of 0.67 mg/mL, whereas the adult mortality assay for C. elegans showed an LC50 of 2.23 mg/mL. These results suggest the acaricidal, repellent, and nematicidal efficacy of essential oil of L. origanoides.