A total of 18 medicinal plants belonging to 12 families have been registered. A general review of the literature on these medicinal plants showed that they are also used in many African countries in the treatment of malaria, such as in Ghana: Carica papaya, Khaya senegalensis, Nauclea latifolia, Azadirachta indica, Psidium guajava ; in Ivory coast: Ocimum gratissum, Entada Africana, Vernonia guineens [13, 14]; in Uganda : Carica papaya; Boswellia papyrifera, vernonia guineensis ; and in Nigeria: Boswellia dalziellii, Eucalyptus globulus, Senna siamea . This consensus among users in different countries reflects the importance of medicinal plants to African populations, and the fact that these same plants are used by different communities for the same purpose could possibly indicate their effectiveness. Previous laboratory studies provide evidence to support the anti-malarial activity of many plant species harvested in the locality of Gamba as shown in Appendix 1 which presents the antiplasmodial activity and phytochemical characteristics that confirm their traditional use.
In general, in vivo antimalarial activity tests in mice infected with P. berghei showed a dose-dependent reduction in parasitemia in mice parasitized with the tested extracts and quinine.
Compared to the Rosanaivo scale, the decocted aqueous extract which gave percentage reductions of 34.84%, 48.36% respectively at doses of 65 and 130 mg/kg body weight had a low activity, while at 260 mg/kg the extract had a moderate activity (52.46%). The antiplasmodial activity of the macerated extract (39.74%) at the 75mg/kg dose reflected a low antiplasmodial activity, compared to the other two doses of 150 and 300 mg/kg, the reduction in parasitemia was 59.41% and 71.79% respectively reflecting a moderate antiplasmodial activity about twice as high as the decocted extract at the 260 mg/kg dose.
At the administration dose of 300 mg/kg, the parasite inhibition by the aqueous macerate was 71.80% whereas at the dose of 10 mg/kg, quinine resulted in 99.18% parasite inhibition. The parasite inhibition of quinine could probably be matched by doubling the dosage and/or optimizing the extraction. The macerate showed better parasitic inhibition than the decocted one. This means that the aqueous decoction was less active than the macerate. This could be related to the boiling temperature, which may have destroyed certain bioactive chemical compounds .
The antimalarial drug of reference remains largely more effective than the macerated extract. This is easily understandable when we know that quinine (a fast-acting schizonticide) is a pure molecule , while the aqueous macerate is an agglomerate of chemical molecules that can act synergistically or develop antagonism. An isolation of the active molecules responsible for the anti-malarial activity, would allow a much more reliable comparative study to be made. At this stage of the study, it would be difficult to make any structure-activity relationship but we can say that the activity observed could be due to all the chemical groups identified in our extracts according to the literature. Indeed certain phytochemical studies carried out on Khaya senegalensis bark have revealed the presence of saponins, tannins, flavonoids, terpenoids, alkaloids, etc[19, 20]. Studies have shown that the alkaloids and terpenoids of the plants would have an activity on plasmodium falciparum by shizonicidal action. A blood schizonticide is an active product against asexual forms of the blood (cause of clinical manifestations) and cures malaria. Alkaloids are believed to inhibit the polymerization of the haemoglobin heme and thus prevent the reproduction of plasmodium. And terpenoids block an enzyme ,Ca++-ATPase which allows the parasite to pump calcium and thus prevent it from developing. . The limoïdes which are terpenoids were indeed highlighted in this plant. . A study showed that limoids from the meliacae family had moderate activity on Plasmodium berghei .
On the other hand, only one in vitro study on khaya senegalensis was found to confer good antiplasmodial activity on the chloroquino-resistant strain of Plasmodium falciparum with an IC50 of 5.5 µg/ml . Moderate in vivo activity may also be due to low oral bioavailability of certain chemical molecules. With these results, Khaya senegalensis cannot exert its activity only by direct action against parasites, the beneficial therapeutic effects claimed by patients could also be due to the anti-inflammatory and immunomodulating activities described for this plant [25, 26].