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Background  Malaria remains a major public health problem, due largely to emergence and widespread  P. falciparum  drug resistance. WHO recommends artemisinine combination based therapy (ACT) to overcome  P. falciparum  drug resistance, but reports of declining ACT efficacy have been published. A thorough understanding of the molecular bases of  P. falciparum  resistance to existing drugs is therefore needed. The aims of this study were to analyze the  in vitro  sensitivity of  P. falciparum  field isolates from Franceville, Gabon, to chloroquine (CQ), mefloquine (MF), dihydroartemisinine (DHA) and monodesethylamodiaquine (MDAQ), and to investigate polymorphisms associated with drug resistance.    Methods  We conducted a cross-sectional study of 53 field isolates. Field isolates sensitivity to CQ, MF, DHA and MDAQ was assessed using the colorimetric DELI test. The  Pfmdr1  codons 86 and 1246,  Pfcrt  (haplotype codon 72 to 76) and the  PfATPAse6  codons 110 and 2694 were analysed by PCR-RFLP. Associations between drug sensitivity and parasite gene polymorphisms were evaluated with the Chi square test, and routine hematological parameters were analyzed with Fisher’s exact test implemented with Epinfo software. In all statistical tests, significance was assumed at p<0.05.    Results  A total of 46  P. falciparum  isolates were successfully cultured  in vitro  and their sensitivity was tested. The proportions of isolates resistant to CQ, MF and MDAQ were 43.5%, 23.4% and 56.5%, respectively. Some isolates (23.9%) had DHA IC 50  values higher than 10 nM. The median IC 50  values were 71.67 (interquartile range (IQR, 1–438.2), 6.59 (IQR, 0.08-96), 64.79 (IQR, 0.09-448) and 6.45 nM (IQR, 0.09-23) for CQ, MF, MDAQ and DHA, respectively. The strongest correlation between diminished DHA sensitivity and MF resistance was observed (r 2 =0.73), followed by correlation between diminished DHA sensitivity and CQ resistance. Cross-resistance between CQ and MF was also observed. The prevalence of the 86Y and 1246Y mutations in  Pfmdr1 , 76T in  Pfcrt , and 110A and 2694T in  PfATPase6  was respectively 42% and 17.1%, 97.8%, and 0% and 22.2%.    Conclusion  These high levels of antimalarial drug resistance in Franceville, Gabon, call for reinforced surveillance of drug efficacy.

In vitroantimalarial susceptibility and molecular markers of drug resistance in Franceville, Gabon