Study of resistance to artemisinins in Plasmodium falciparum isolates from Kilifi County

Abstract

Malaria is a health problem and drug resistance to antimalarial poses a great challenge to its treatment and control. Having a rapid activity against malaria parasites, artemisinins are the front line antimalarials. However, already there are reports on reduced response to artemisinins. Thus it’s important to monitor resistance in malaria risky areas. Merozoite surface protein (MSP) 1 and 2 genotyping has shown difference between isolates from primary and recurrent infections but how this relates to their in vitro sensitivity is not known. The study aimed at determining resistance of P. falciparum to artemisinins in Kilifi County. Specifically to determine: 1. in vitro sensitivity of P. falciparum to artemisinins; 2. the difference between their in vitro activity with that of other antimalarial drugs; 3. the existence of in vitro cross-resistance; and 4. whether there is difference in the in vitro response to artemisinins in isolates from primary and recurrent infection. Parasites isolates were cultured in vitro and drug response assay carried out by subculturing them in various drug concentrations. In vitro activity was determined as the drug concentration that inhibited 50% of parasite growth (IC50) using SYBR green I microtest. Kruskal Wallis and Dunn’s post test were used to compare the in vitro activity of artemisinins and that of other antimalarial drugs. Mann Whitney test was used to determine the difference in the in vitro response of the isolates from initial and recurrent infection. Spearman correlation analysis was used to determine existence of in vitro cross-resistance patterns between artemisinins and other antimalarials. The mean IC50s (in nM) of Dihydroartemisinin (DHA), Piperaquine (PQ), Lumefantrine (LMF), Chloroquine (CQ), Quinine (Q), Pyrimethamine (PYR), Desethylamodiaquine (DE-A) and Mefloquine (MFQ) were 1.861, 30.34, 46.5, 24.29, 46.7, 18074, 37.8 and 41.7 nM respectively. There was significant difference in the in vitro activities of the antimalarial drugs, DHA being the most active drug. There was no significant difference in the in vitro response of the isolates from initial and recurrent malarial infections towards the antimalarials. There was no significant correlation in the IC50s of the eight antimalarial drugs. Therefore, artemisinins are still active in Kilifi County; more active than other standard antimalarials and no cross-resistance was observed with other antimalarials. Consequently, as ACTs they should be continued to be used as first line antimalarials.