In vitro ovicidal activity of Baccharis conferta Kunth against Haemonchus contortus.

The indiscriminate use of chemical drugs to deworm livestock tends to trigger an anthelmintic resistance problem. In this context, the use of plant extracts rich in secondary metabolites could be an alternative method for the control of gastrointestinal nematodes. Baccharis conferta Kunth is a native plant species from Mexico that is widely used by several ethnic groups as forage for farm animals and medicinally to treat gastrointestinal diseases such as acute stomach ache, dysentery, diarrhoea, vomiting, indigestion, colic, intestinal spasms, urinary problems, and cramps. The aim of the present study was to isolate and characterise the ovicidal constituents of B. conferta and to determine a possible mode of action against Haemonchus contortus. The ovicidal activity was determined using the egg hatching inhibition test (EHI) to assess the methanol extract obtained from B. conferta foliage. The dry extract was partitioned (water/ethyl acetate) to obtain an ethyl acetate (BcEtOAc-F) and aqueous fraction. BcEtOAc-F showed an ovicidal activity of 72.32% EHI at 1 mg/mL. The chromatographic fractionation of BcEtOAc-F resulted in three active sub-fractions with higher ovicidal activity: BcC1R4 (99.15% EHI at 1.0 mg/mL); BcC1R5 (92.51% EHI at 0.75 mg/mL); and BcC1R8 (96.8% EHI at 3.0 mg/mL). Chemical analysis of the BcC1R4 fraction allowed the identification of the major active compound, isokaempferide (1, 98.06% EHI at 1 mg/mL). While, 4,5-di-O-acid caffeoylquinic (3; 96.8% EHI at 3 mg/mL) and an inactive flavone (vicenin-2, 2) were identified as the main compounds in BcC1R8. Chemical characterisation of the isolated compounds was performed via spectroscopic (NMR) and spectrometric (UPLC-MS) analyses. Additionally, the environmental and confocal scanning microscopy analyses revealed that isokaempferide was able to cross the eggshell layer without breaking it and attach itself to the embryo, causing its death. The flavonol, isokaempferide, and the hydroxycinamic acid, 4,5-di-O-caffeoylquinic, displayed powerful ovicidal effects, proving to be a potential alternative for the development of a phytodrug for the control of haemonchosis.