Genetic variation of the dihydrofolate reductase gene in Plasmodium vivax in Snoul, northeastern Cambodia.

In Plasmodium vivax, pyrimethamine resistance is associated with amino acid substitutions Ser117Asn and Ser58Arg in dihydrofolate reductase (DHFR), which correspond to Ser108Asn and Cys59Arg in the Plasmodium falciparum homolog, respectively. Sequence variations within the DHFR domain of 32 P. vivax isolates from Snoul, Cambodia, were analyzed by direct sequencing of polymerase chain reaction (PCR) products. Sequence polymorphisms within the entire DHFR domain were limited to codons 58 and 117 and GGDN tandem repeat units. A large majority (30 of 32) of isolates were characterized to be double mutants (Arg-58 and Asn-117) and associated with the presence of two GGDN repeat units. Only one isolate was of wild-type with three GGDN repeat units, and an additional isolate was of mixed type. Our data suggest that most Cambodian P. vivax isolates display double dhfr mutations associated with pyrimethamine resistance, as in the neighboring countries in Southeast Asia. Further molecular characterization of P. vivax isolates from different endemic areas may be a useful alternative approach to establish the epidemiology of drug-resistant malaria.

Efficacy and effectiveness of the combination of sulfadoxine/pyrimethamine and a 3-day course of artesunate for the treatment of uncomplicated falciparum malaria in a refugee settlement in Zambia.

In the Maheba Refugee Settlement, in the clinics supported by Medecins Sans Frontieres, all children aged up to 5 years with a confirmed diagnosis of uncomplicated falciparum malaria are treated with the combination of sulfadoxine/pyrimethamine (SP) and artesunate (AS). We compared the treatment's efficacy and effectiveness. Patients were randomized in order to receive the treatment supervised (efficacy) or unsupervised (effectiveness). Therapeutic response was determined after 28 days of follow up. The difference between recrudescence and re-infection was ascertained by polymerase chain reaction (PCR). We also assessed genetic markers associated to SP resistance (dhfr and dhps). Eighty-five patients received treatment under supervision and 84 received it unsupervised. On day 28, and after PCR adjustment, efficacy was found to be 83.5% (95% CI: 74.1-90.5), and effectiveness 63.4% (95% CI: 52.6-73.3) (P < 0.01). Point mutations on dhfr (108) and dhps (437) were found for 92.0% and 44.2% respectively of the PCR samples analysed. The significant difference in therapeutic response after supervised and unsupervised treatment intake can only be explained by insufficient patient adherence. When implementing new malaria treatment policies, serious investment in ensuring patient adherence is essential to ascertain the effectiveness of the new treatment schedules.