Molecular monitoring of Plasmodium falciparum resistance to artemisinin in Tanzania

Resistance to antimalarials is a major drawback in effective malaria control in sub-Saharan Africa. Plasmodium falciparum has developed high levels of resistance to the cheap and safe chloroquine (CQ) and to sulfadoxine-pyrimethamine (SP) [1,2]. Therefore, artemisinin-based combination therapy (ACT) is recommended for use in the whole of sub-Saharan Africa [3,4]. Fifteen out of 43 sub-Saharan African countries have already adopted artesunate + amodiaquine as first-line drug and the rest are at various stages of preparation for changes to the same regimen or to artemether + lumefantrine. Following increased SP resistance in Tanzania [5], the country has revised its malaria treatment policy to adopt artemether+lumefantrine. This change is supposed to be implemented over the whole country from December 2006. To date no relevant clinical resistance to artemisinins has been reported. However, the long-term usefulness of ACT in high transmission areas remains unclear [6]. Therefore, as ACT is becoming widely used in sub-Saharan Africa, the need for regular and comprehensive surveillance of resistance has been recognized. This should include in vitro and in vivo drug efficacy assays, pharmacokinetic analyses and the monitoring of molecular markers associated with resistance to the various components of ACTs.Recently it was hypothesized, and later proved, that artemisinins interact [7] and selectively inhibit [8] PfATPase6, the only SERCA-type Ca2+-ATPase in the P. falciparum genome. A subsequent in vitro study in French Guyana showed that P. falciparum with elevated IC50 values for artemisinins shared specific point mutations at codon S769N of the ATPase6 locus. In addition, ATPase6 A623E and E431K mutations were also associated with reduced P. falciparum susceptibility to artemisinins [9]. This study suggested that documentation of these mutations may indicate emergence of P. falciparum artemisinin resistance in the field. Therefore, the aim of this study was to assess an