Natural Products against Human and Veterinary Trichomonads: From In Vitro Activity to Future Therapeutic Perspectives

Pathogenic trichomonads are flagellated protozoan parasites of the urogenital and digestive tracts of humans and animals. These organisms impose substantial health and economic burdens on the world. Trichomonas vaginalis causes human urogenital trichomoniasis, the most common nonviral sexually transmitted infection worldwide, and has been associated with adverse reproductive outcomes and increased risk of HIV transmission. In animals, Trichomonas gallinae causes avian trichomoniasis, a disease of the upper digestive tract that may impair feeding, compromise survival, and contribute to bird population declines, whereas Tritrichomonas foetus is responsible for bovine trichomoniasis, a major cause of cattle production losses. Despite their importance, therapeutic options remain limited. Human and avian trichomoniasis still rely on 5-nitroimidazoles, but drug resistance and regulatory restrictions have become important concerns, whereas no approved pharmacological treatment is currently available for bovine trichomoniasis, and infected animals are culled. In this context, natural products have emerged as valuable sources of new antitrichomonal agents. This Review summarizes 84 studies published between 2016 and 2026 investigating natural products against T. vaginalis, T. gallinae, and T. foetus, including plant-derived extracts and fractions, essential oils, isolated compounds, microbial metabolites, and nanotechnology-based formulations. Although several products displayed relevant antitrichomonal activity, most evidence remains restricted to in vitro studies, with comparatively few in vivo evaluations and no clinical validation of natural-product-derived candidates for trichomoniasis. Overall, natural products represent a chemically diverse and still underexplored source of antitrichomonal leads, but further validation of their selectivity, pharmacological properties, and in vivo efficacy is required before their therapeutic potential can be established.