Phytotherapeutic potential of Lamiaceae essential oils and their monoterpenes against Giardia duodenalis.

Lamiaceae and Asteraceae plant species have been widely used in Mediterranean ethnomedicine for gastrointestinal disorders. They are also known for their antioxidant, anti-inflammatory, anti-bacterial, anti-parasite, and anti-virus properties. Giardia duodenalis is the most prevalent intestinal protozoon in children and young dogs worldwide. Its zoonotic potential and frequent therapeutic failures with nitroimidazoles underscore the urgent need for alternative treatments. This study investigated the antigiardial activity of essential oils (EOs) from 22 medicinal plants belonging to Lamiaceae and Asteraceae, together with their major constituents. EO composition was determined by a metabolomic approach (GC-MS). Parasite metabolic activity was assessed using the MTT assay, and ultrastructural changes were examined by Transmission Electron Microscopy. The strongest antigiardial effects were observed with Lavandula luisieri, Thymus vulgaris, Mentha suaveolens, Satureja montana (IC50 <25), L. lanata, and T. zygis, (IC50= 27.9-71.5 µg/ml). The highest selective indexes were obtained with γ-terpinene, caryophyllene oxide, carvacrol and thymol (SI≥1.3-2.4). Synergistic interactions were detected with linalyl acetate and linalool (present in Lavandula EOs), linalyl acetate with ρ-cymene or thymol, or combinations of ρ-cymene, γ-terpinene, thymol, and carvacrol (present in Satureja EOs). Transmission Electron Microscopy revealed membranolysis, enlarged periplasmic vacuoles, and cytoplasmic loss in trophozoites exposed to γ-terpinene after 1 h. These findings provide phytotherapeutic evidence supporting essential oils from Lavandula, Mentha, Thymus, and Satureja as promising antigiardial agents. Their main components γ-terpinene, caryophyllene oxide, carvacrol and thymol could have potential applications in veterinary parasitology.