Haemonchus contortus and Trichostrongylus colubriformis are among the most important parasitic nematodes of small ruminants. Caenorhabditis elegans, a free-living nematode, is used as a modelfor evaluating anthelmintic activity of a variety of test substances. Extracts of several medicinal plants
are useful in vitro and in vivo against nematode development. Extracts of Curtisia dentata, a South
African medicinal plant, and compounds isolated from leaves of this plant were investigated for anthelmintic activity against T. colubriformis, H. contortus and C. elegans. The acetone and dichloromethane extracts were active against all nematodes at concentrations as low as 160 μg/mℓ. Betulinic acid and lupeol were active against the parasitic nematodes only at the high concentrations of 1 000 and 200 μg/mℓ, respectively. All compounds were effective against C. elegans with active concentrations
as low as 8 μg/mℓ. Betulinic acid was less active than lupeol and ursolic acid against C. elegans.
The acetone and dichloromethane extracts were also active against C. elegans with a concentration
of 0.31 mg/mℓ resulting in almost 80 % inhibition of larval motility. The use of free-living nematodes
may provide information on the activity of potential anthelmintics against parasitic nematodes. Extracts
of various medicinal plant species may provide solutions to ill-health of small ruminants caused by
parasitic nematodes in poor communities of southern Africa.