Indigenous rural communities in the tropics manage parasitic diseases, like malaria and leishmaniasis, using herbal drugs. The efficacy, dosage, safety and active principles of most of the herbal preparations are not known. Extracts from 6 selected plant species, used as medicinal plants by indigenous local communities in Kenya, were screened for in vitro anti-plasmodial and anti-leishmanial activity, against 2 laboratory-adapted Plasmodium falciparum isolates (D6, CQ-sensitive and W2, CQ-resistant) and Leishmania major (IDU/KE/83 = NLB-144 strain), respectively. The methanol extract of Suregada zanzibariensis leaves exhibited good anti-plasmodial activity (IC50 4.66 ± 0.22 and 1.82 ± 0.07 μg/ml for D6 and W2, respectively). Similarly, the methanol extracts of Albizia coriaria (IC50 37.83 ± 2.11 μg/ml for D6) and Aspergillus racemosus (32.63 ± 2.68 and 33.95 ± 2.05 μg/ml for D6 and W2, respectively) had moderate anti-plasmodial activity. Acacia tortilis (IC50 85.73 ± 3.36 μg/ml for W2) and Albizia coriaria (IC50 71.17 ± 3.58 μg/ml for W2) methanol extracts and Aloe nyeriensis var kedongensis (IC50 87.70 ± 2.98 and 67.84 ± 2.12 μg/ml for D6 and W2, respectively) water extract exhibited mild anti-plasmodial activity. The rest of the extracts did not exhibit any anti-plasmodial activity. Although the leishmanicidal activity of extracts were lower than for pentosam (80%), reasonable activity was observed for Aloe nyeriensis methanol (68.4 ± 6.3%), Albizia coriara water (66.7 ± 5.0%), Maytenus putterlickoides methanol (60.0 ± 6.23%), Asparagus racemosus methanol and water (58.3 ± 8.22 and 56.8 ± 6.58%, respectively), Aloe nyeriensis water (53.3 ± 5.1%) and Acacia tortilis water (52.9 ± 6.55%) extracts at 1000 μg/ml. Leishmania major infected macrophages treated with methanol extracts of Suregada zanzibariensis and Aloe nyeriensis var kedongensis and Pentostam® had infection rates of 28 ± 2.11, 30 ± 1.22 and 40 ± 3.69%, respectively at 1000 μg/ml, indicating better anti-leishmanial activity for the extracts. The methanol extract of Albizia coriara (44.0 ± 3.69%) and aqueous extracts of Asparagus racemosus (42 ± 3.84%) and Acacia tortilis (44 ± 5.59%) had similar activity to pentosam®. Multiplication indices for Leishmania major amastigotes treated with methanol extracts of Albizia coriaria, Suregada zanzibariensis and Aloe nyeriensis var kedongensis, aqueous extract of Acacia tortilis and pentosam® were 28.5 ± 1.43, 29.4 ± 2.15, 31.1 ± 2.22, 35.9 ± 3.49 and 44.0 ± 3.27%, respectively, at 1000 μg/ml, confirming better anti-leishmanial activity for the extracts. Aqueous extracts of Aloe nyeriensis (46.7 ± 3.28%) and Albizia coriaria (47.5 ± 3.21%) had similar activity level to pentosam®. The plant extracts have better inhibitory activity while pentosam® has better leishmanicidal activity. All extracts exhibited very low cytotoxicity (CC50 > 500 μg/ml) against human embryonic lung fibroblast (HELF) cells. The investigations demonstrated the efficacy and safety of some extracts of plants that are used by rural indigenous communities for the treatment of parasitic diseases. © 2009.
