Vivax malaria is widespread and resistance has been described for
chloroquine and
sulfadoxine-pyrimethamine. We report on evidence of failure of
mefloquine prophylaxis in a French soldier who contracted Plasmodium vivax in French Guyana, South America. Despite regular weekly
mefloquine prophylaxis (250 mg/d), the patient presented with a first episode of
vivax malaria, which was treated by
chloroquine alone, then experienced a second crisis in France. The reappearance of the parasites occurred one day after the end of prophylaxis, confirming parasitological and clinical resistance in a non-immune patient.
Mefloquine was detected by a liquid chromatography assay in plasma at a level of 1062 ng/ml, which was higher than the expected concentration after five months of weekly prophylaxis. This isolate had no single nucleotide polymorphisms of the pvmdr1 gene at seven allele positions: pvmdr1 N91, Y189, Y976, S1071, F1076, N1079 and D1291, corresponding to
codons 86, 184, 939, 1034, 1039, 1042 and 1246 in P. falciparum. This observation of failure of
mefloquine prophylaxis against P. vivax, when added to previously reported
chloroquine and
atovaquone-proguanil failure, strengthens the case for re-evaluating
drug policies for
vivax malaria and the need for continuous research on molecular markers of drug resistance.