title: Plasmodium vivax and Plasmodium falciparum ex vivo susceptibility to anti-malarials and gene characterization in Rondônia, West Amazon, Brazil.
abstract: BACKGROUND
  Chloroquine (CQ), a cost effective antimalarial drug with a relatively good safety profile and therapeutic index, is no longer used by itself to treat patients with Plasmodium falciparum due to CQ-resistant strains. P. vivax, representing over 90% of malaria cases in Brazil, despite reported resistance, is treated with CQ as well as with primaquine to block malaria transmission and avoid late P. vivax malaria relapses. Resistance to CQ and other antimalarial drugs influences malaria control, thus monitoring resistance phenotype by parasite genotyping is helpful in endemic areas.
  
  
  METHODS
  A total of 47 P. vivax and nine P. falciparum fresh isolates were genetically characterized and tested for CQ, mefloquine (MQ) and artesunate (ART) susceptibility in vitro. The genes mdr1 and pfcrt, likely related to CQ resistance, were analyzed in all isolates. Drug susceptibility was determined using short-term parasite cultures of ring stages for 48 to 72 hour and thick blood smears counts. Each parasite isolate was tested with the antimalarials to measure the geometric mean of 50% inhibitory concentration.
  
  
  RESULTS
  The low numbers of  P. falciparum isolates reflect the species prevalence in Brazil; most displayed low sensitivity to CQ (IC50 70 nM). However, CQ resistance was rare among P. vivax isolates (IC50 of 32 nM). The majority of P. vivax and P. falciparum isolates were sensitive to ART and MQ. One hundred percent of P. falciparum isolates carried non-synonymous mutations in the pfmdr1 gene in codons 184, 1042 and 1246, 84% in codons 1034 and none in codon 86, a well-known resistance mutation. For the pfcrt gene, mutations were observed in codons 72 and 76 in all P. falciparum isolates. One P. falciparum isolate from Angola, Africa, showing sensitivity to the antimalarials, presented no mutations. In P. vivax, mutations of pvmdr1 and the multidrug resistance gene 1 marker at codon F976 were absent.
  
  
  CONCLUSIONS
  All P. falciparum Brazilian isolates showed CQ resistance and presented non-synonymous mutations in pfmdr1 and pfcrt. CQ resistant genotypes were not present among P. vivax isolates and the IC50 values were low in all samples of the Brazilian West Amazon.
authors.forename: Anna Caroline C
authors.initials: AC
authors.lastname: Aguiar
authors.forename: Dhelio B
authors.initials: DB
authors.lastname: Pereira
authors.forename: Nayra S
authors.initials: NS
authors.lastname: Amaral
authors.forename: Luiz
authors.initials: L
authors.lastname: De Marco
authors.affiliation: Laboratório de Malária, Centro de Pesquisas René Rachou, FIOCRUZ, Av, Augusto de Lima 1715, 30190-002 Belo Horizonte, MG, Brazil. akrettli@cpqrr.fiocruz.br.
authors.forename: Antoniana U
authors.initials: AU
authors.lastname: Krettli
mesh_terms: D000328:Adult; D000962:Antimalarials / Q000494:pharmacology*; D037621:Artemisinins / Q000494:pharmacology; D000077332:Artesunate; D001938:Brazil; D002738:Chloroquine / Q000494:pharmacology; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics*; D004351:Drug Resistance; D005260:Female; D005838:Genotype; D006801:Humans; D020128:Inhibitory Concentration 50; D008288:Malaria / Q000469:parasitology; D008297:Male; D015767:Mefloquine / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics; D020125:Mutation, Missense; D021261:Parasitic Sensitivity Tests; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D010966:Plasmodium vivax / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D015800:Protozoan Proteins / Q000235:genetics
chemical_list: D000962:Antimalarials; D037621:Artemisinins; D000077332:Artesunate; D002738:Chloroquine; D016054:DNA, Protozoan; D015767:Mefloquine; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015800:Protozoan Proteins; C513498:Mdr1 protein, Plasmodium falciparum; C541684:Mdr1 protein, Plasmodium vivax; C416369:PfCRT protein, Plasmodium falciparum