Pharmacological investigation of medicinal plants used traditionally in southern Africa to treat gastrointestinal nematode infections of small ruminants

Abstract

Haemonchus contortus is a major gastrointestinal helminth parasite causing haemonchiasis in production animals. Infections are characterized by fever, anaemia, weight loss and ultimately death. Haemonchiasis is a serious economic challenge globally resulting in poor reproductive efficiency, increased susceptibility to bacterial and fungal infections, as well as low production of wool, milk and meat. Treatments with synthetic drugs are currently the only effective way to control the infestation. Albendazole is a drug of choice against this parasite; it acts by binding to tubulins and causes depolymerisation of microtubules. No other anthelminthic compounds of comparable efficacy are available yet and there is a critical need to find alternative drugs. An alternative strategy is to investigate ethnoveterinary plants with putative anthelminthic properties.

The aim of this study was to evaluate selected plant extracts for anthelmintic activity in vitro against Haemonchus contortus, as well as antifungal activity to determine correlations in these activities. Cytotoxicity of the plant extracts was also tested, and isolation of compounds was performed. The crude extracts of Diospyros whyteana and Peddiea africana showed low cytotoxicity with LC50 greater than 1 mg/ml. Good antifungal activity was observed in D. whyteana, Peddiea africana and Schotia brachypetala with MICs ranging from 40-160 mg/ml against Candida albicans and selectivity index (SI) values from 6.25-12.5. In the egg hatch inhibition assay, D. whyteana had good results with EC50=0.7377 mg/ml for acetone while water extracts were 1.508, thus the SI ranged from 0.66 to 1.35. Water extracts showed better anthelmintic activity compared to acetone extracts of D. whyteana, P. africana and Schotia brachypetala. The extracts had good activity in the egg hatch assay, good antifungal activity, and they were non-toxic to Vero cells. Four bioactive compounds have been isolated from Diospyros whyteana with excellent activity against Candida albicans and the structures of these are being determined.