Sensitivity of two in vitro assays for evaluating plant activity against the infective stage of Haemonchus contortus strains.

The sensitivity of larval paralysis assay (LPA) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide-formazan (MTT-formazan) assay was compared to evaluate the anthelmintic activity of plant extracts. In this study, the methanolic extract of Azadirachta indica (neem) was evaluated for its activity against the infective-stage larvae (L(3)) of susceptible and resistant Haemonchus contortus strains using the two aforementioned assays. In both in vitro assays, the same serial concentrations of the extract were used, and the median lethal concentrations were determined to compare the sensitivity of both assays. The results revealed a significant difference (P < 0.05) in the sensitivity of the LPA and the MTT-formazan assay. The MTT-formazan assay is more feasible for practical applications because it measured the L(3) mortality more accurately than LPA. This study may help find a suitable assay for investigating the anthelmintic activity of plant extracts against trichostrongylid nematodes.