Emergence of P. vivax resistance to chloroquine in French Guiana.

In South America, Plasmodium vivax resistance to chloroquine was recently reported in Brazil and Bolivia. The objective of this study was to collect data on chloroquine resistance in French Guiana by associating a retrospective evaluation of the therapeutic efficacy and an analysis of recurrent parasitemia from any patients.Patients with P. vivax infection, confirmed by microscopy and temperature ≥37.5°C, were retrospectively identified at Cayenne Hospital between 2009 and 2015. Follow-up and treatment responses were performed according to the World Health Organization protocol. Parasite resistance was confirmed after dosage of plasmatic concentration of chloroquine and microsatellite characterization. The pvmdr1 and pvcrt-o genes were analysed for sequence and gene copy-number variation.Among the 172 patients followed for 28 days, 164 presented adequate clinical and parasitological responses. Eight cases of treatment failures were identified (4.7%, n=8/172), all after 14 days. The therapeutic efficacy of chloroquine was estimated at 95.3% (95% CI 92.5-98.1, n=164/172). Among the eight failures, five were characterized: two cases were true P. vivax chloroquine resistance (1.2%, 95% CI 0-2.6, n=2/172) and three cases were found with subtherapeutic concentrations of chloroquine. No particular polymorphism in the Plasmodium vivax pvmdr1 and pvcrt-o genes was identified in the resistant parasites.This identified level of resistance of P. vivax to chloroquine in French Guiana does not require a change in therapeutic recommendations. However, primaquine should be administered more frequently to limit the spread of resistance and there is still a need for a reliable molecular marker to facilitate the monitoring of resistance to chloroquine.