CHARACTERIZATION OF PLASMODIUM-FALCIPARUM ISOLATED FROM THE AMAZON REGION OF BRAZIL - EVIDENCE FOR QUININE RESISTANCE

The prevalence and severity of drug-resistant malaria is emerging rapi dly in the Amazon basin of Brazil. In support of clinical trials using the new antimalarial drug combination of atovaquone and proguanil, we performed in vitro drug sensitivities, molecular characterization of parasite populations using the circumsporozoite protein, merozoite sur face antigen-1 (MSA-1), and MSA-2 markers, and an analysis of the Plas modium falciparum multidrug resistance (pfmdr1) gene sequence and copy number in 26 isolates of P. falciparum obtained in a gold-mining ende mic area in Peixoto de Azevedo, Mate Grosso State. All 26 isolates wer e found to be resistant to chloroquine (50% inhibitory concentration [ IC50] = 100-620 nM) and sensitive to mefloquine (IC50 < 23 nM) and hal ofantrine (IC50 < 6 nM). The isolates also show reduced susceptibility to quinine (IC50 = 48-280 nM). Sequence analysis of the pfmdr1 gene r evealed Asn, Phe, Cys, Asp, and Tyr in positions 86, 184, 1034, 1042, and 1246, respectively. These point mutations were similar to that pre viously described in other Brazilian isolates. Southern blot analysis revealed no amplification of the pfmdr1 gene. These results suggest th at three different mechanisms for drug resistance exist for chloroquin e, mefloquine, and quinine.