title: Chloroquine efficacy studies confirm drug susceptibility of Plasmodium vivax in Chennai, India.
abstract: BACKGROUND
  Assessing the Plasmodium vivax burden in India is complicated by the potential threat of an emerging chloroquine (CQ) resistant parasite population from neighbouring countries in Southeast Asia. Chennai, the capital of Tamil Nadu and an urban setting for P. vivax in southern India, was selected as a sentinel site for investigating CQ efficacy and sensitivity in vivax malaria.
  
  
  METHODS
  CQ efficacy was evaluated with a 28-day in vivo therapeutic study, while CQ sensitivity was measured with an in vitro drug susceptibility assay. In both studies, isolates also underwent molecular genotyping to investigate correlations between parasite diversity and drug susceptibility to CQ. Molecular genotyping included sequencing a 604 base pair (bp) fragment of the P. vivax multidrug resistant gene-1 (Pvmdr1) for single nucleotide polymorphisms (SNPs) and also the amplification of eight microsatellite (MS) loci located across the genome on eight different chromosomes.
  
  
  RESULTS
  In the 28-day in vivo study (N=125), all subjects were aparasitaemic by Day 14. Passive case surveillance continuing beyond Day 28 in 22 subjects exposed 17 recurrent infections, which ranged from 44 to 148 days post-enrollment. Pvmdr1 sequencing of these recurrent infections revealed that 93.3% had identical mutant haplotypes (958M/Y976/1076L) to their baseline Day 0 infection. MS genotyping further revealed that nine infection pairs were related with ≥ 75% haplotype similarity (same allele at six or more loci). To test the impact of this mutation on CQ efficacy, an in vitro drug assay (N=68) was performed. No correlation between IC50 values and the percentage of ring-stage parasites prior to culture was observed (r(sadj): -0.00063, p = 0.3307) and the distribution of alleles among the Pvmdr1 SNPs and MS haplotypes showed no significant associations with IC50 values.
  
  
  CONCLUSIONS
  Plasmodium vivax was found to be susceptible to CQ drug treatment in both the in vivo therapeutic drug study and the in vitro drug assay. Though the mutant 1076 L of Pvmdr1 was found in a majority of isolates tested, this single mutation did not associate with CQ resistance. MS haplotypes revealed strong heterogeneity in this population, indicating a low probability of reinfection with highly related haplotypes.
authors.forename: Sneh
authors.initials: S
authors.lastname: Shalini
authors.forename: Saumyadripta
authors.initials: S
authors.lastname: Chaudhuri
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Sutton
authors.forename: Neelima
authors.initials: N
authors.lastname: Mishra
authors.forename: Nalini
authors.initials: N
authors.lastname: Srivastava
authors.forename: Joseph K
authors.initials: JK
authors.lastname: David
authors.forename: K John
authors.initials: KJ
authors.lastname: Ravindran
authors.forename: Jane M
authors.initials: JM
authors.lastname: Carlton
authors.affiliation: National Institute of Malaria Research (Indian Council of Medical Research), National Institute of Epidemiology Campus, Second Main Road, Tamil Nadu Housing Board, Ayapakkam, Chennai 600 077, Tamil Nadu, India. alexeapen@yahoo.com.
authors.forename: Alex
authors.initials: A
authors.lastname: Eapen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000962:Antimalarials / Q000494:pharmacology*; D002648:Child; D002738:Chloroquine / Q000494:pharmacology*; D004351:Drug Resistance; D005260:Female; D006801:Humans; D007194:India; D016780:Malaria, Vivax / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism; D021261:Parasitic Sensitivity Tests; D010966:Plasmodium vivax / Q000187:drug effects* / Q000235:genetics*; D011110:Polymorphism, Genetic; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D055815:Young Adult
chemical_list: D000962:Antimalarials; D002738:Chloroquine; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015800:Protozoan Proteins; C541684:Mdr1 protein, Plasmodium vivax