In vitro reduction of Plasmodium falciparum gametocytes by Artemisia spp. tea infusions

In this study, we showed in vitro evidence that supports the efficacy of A. annua and A. afra tea infusions used in a 2015 clinical trial not only for clearing asexual Plasmodium falciparum parasites, but also for eliminating sexual gametocytes. P. falciparum NF54 was grown in vitro, synchronized, and induced to form gametocytes using N-acetylglucosamine. Cultures during asexual, early, and late stage gametogenesis were treated with artemisinin, methylene blue, and Artemisia annua and A. afra tea infusions (5g DW/L) using cultivars that contained 0-283 M artemisinin. Asexual parasitemia and gametocytemia were analyzed microscopically. Gametocyte morphology was also scored. Markers of early (PfGEXP5) and late stage (Pfs25) gametocyte gene expression were also measured using RT-qPCR. Both A. annua and A. afra tea infusions reduced gametocytemia in vitro, and the effect was mainly artemisinin dependent. Expression levels of both marker genes were reduced with the effect mainly attributed to artemisinin content of the our tested Artemisia cultivars. Tea infusions of both species also inhibited asexual parasitemia and although mainly artemisinin dependent, there was a weak antiparasitic effect from artemisinin-deficient A. afra. These results showed that A. annua and to a lesser extent, A. afra, inhibited parasitemia and gametogenesis in vitro, and results are consistent with earlier observed clinical results.