Antimalarial effect of essential volatile oils from Nigerian medicinal plants on Plasmodium yoelii nigeriensis (in-vivo) and Plasmodiun falciparum (in-vitro)

Three essential volatile oils from Citrus aurantifolia, Citrus sinensis and Callistemon rigidus leaves and fruit peels were examined for their antimalarial property in-vivo and in-vitro. About 47, 36, and 14% of the asexual erythrocytic stages of Plasmodium yoelii nigeriensis were inhibited with various doses of oil after the 4-day schizonticidal test by Callistemon rigidus, Citrus aurantifolia and Citrus sinensis respectively. In-vitro activity of oil suspensions against P. falciparum also produced significant inhibition in parasites growth. IC₅₀ values of 8.0; 17.0; 54.6ng/ml indicated that Callistemon rigidus, Citrus aurantifolia and Citrus sinensis followed the same order of activity as shown in the in-vivo study. However, the oils ability to prolong the survival of highly parasitemic mice was not the same in all the animals. Callistemon rigidus, Citrus aurantifolia and Citrus sinensis prolonged the survival time of animals between 18.0 and 29.6 days, 16.2 and 20.2 days and 3.8 and 8.6 days respectively, compared to the control group that survived till 15.6 days. Temperature of the animals monitored showed that the three oils lowered the temperature of treated infected animals as compared to the control. Our results suggest that Callistemon rigidus, and Citrus aurantifolia are promising new antimalarial agents.