ETHNOPHARMACOLOGICAL RELEVANCE : Extracts of plant species, used traditionally to treat
malaria, have been extensively investigated for their activity against Plasmodium
intraerythrocytic asexual parasites in search of new antimalarial drugs. However, less effort
has been directed towards examining their efficacy in blocking transmission. Here, we report
the results of the in vitro screening of extracts from eight selected plant species used
traditionally to treat malaria in South Africa for activity against P. falciparum NF54 early and
late stage gametocytes. The species used were Khaya anthotheca, Trichilia emetica, Turraea
floribunda, Leonotis leonurus, Leonotis leonurus ex Hort, Olea europaea subsp. Africana,
Catha edulis and Artemisia afra.
AIM OF STUDY : To investigate the activities of extracts from plant species traditionally used
for malaria treatment against P. falciparum gametocytes.
MATERIAL AND METHODS : Air-dried and ground plant leaves were extracted using acetone.
Primary two point in vitro phenotypic screens against both early and late stage gametocytes
were done at 10 and 20 μg/ml followed by full IC50 determination of the most active extracts.
Inhibition of gametocyte viability in vitro was assessed using the parasite lactate
dehydrogenase (pLDH) assay.
RESULTS : Of the eight crude acetone extracts from plant species screened in vitro, four had
good activity with over 50-70% inhibition of early and late stage gametocytes’ viability at 10
and 20 μg/ml, respectively. Artemisia afra (Asteraceae), Trichilia emetica (Meliaceae) and
Turraea floribunda (Meliaceae) were additionally highly active against both gametocyte
stages with IC50 values of less than 10 μg/ml while Leonotis leonurus ex Hort (Lamiaceae)
was moderately active (IC50<20 μg/ml). The activity of these three highly active plant species
was significantly more pronounced on late stage gametocytes compared to early stages.
CONCLUSION : This study shows the potential transmission blocking activity of extracts from
selected South African medicinal plants and substantiates their traditional use in malaria
control that broadly encompasses prevention, treatment and transmission blocking. Further
studies are needed to isolate and identify the active principles from the crude extracts of A.
afra, T. emetica and T. floribunda, as well as to examine their efficacy towards blocking
parasite transmission to mosquitoes.