title: Chloroquine resistant Plasmodium vivax: in vitro characterisation and association with molecular polymorphisms.
abstract: BACKGROUND
  Treatment failure of chloroquine for P. vivax infections has reached high levels in the eastern provinces of Indonesia, however, in vitro characterization of chloroquine resistance and its associated molecular profile have yet to be determined.
  
  
  METHODS
  Using a modified schizont maturation assay we investigated the in vitro chloroquine susceptibility profile and molecular polymorphisms of P. vivax isolates collected from Papua, Indonesia, where high levels of clinical chloroquine treatment failure have been reported, and from Thailand, where chloroquine treatment is generally effective.
  
  
  RESULTS
  The geometric mean chloroquine IC(50) for P. vivax isolates from Papua (n = 145) was 312 nM [95%CI: 237-411 nM] compared to 46.8 nM [95%CI: 34.7-63.1 nM] from Thailand (n = 81); p<0.001. Correlating with the known clinical efficacy of the area, a cut off for chloroquine resistance was defined as 220 nM, a level exceeded in 13.6% (11/81) of Thai isolates and 65% (94/145) of Papuan isolates; p<0.001. Several sequence polymorphisms in pvcrt-o and pvmdr1, and difference in pvmdr1 copy number were identified. A Y976F mutation in pvmdr1 was present in 96% (123/128) of Papuan isolates and 25% (17/69) of Thai isolates; p<0.001. Overall, the geometric mean chloroquine IC(50) in isolates with the Y976F mutation was 283 nM [95%CI: 211-379], compared to 44.5 nM [95%CI: 31.3-63.4] in isolates with the wild type; p< 0.001. Pvmdr1 amplification occurred in 23% (15/66) of Thai isolates compared to none (0/104) of Indonesian isolates (p<0.001), but was not associated with increased chloroquine resistance after controlling for geographical location.
  
  
  CONCLUSIONS
  In vitro susceptibility testing of P. vivax discriminates between populations with differing levels of clinical efficacy of chloroquine. The pvmdr1 polymorphism at Y976F may provide a useful tool to highlight areas of emerging chloroquine resistance, although further studies defining its clinical correlates are needed.
authors.affiliation: International Health Program, Infectious Diseases Division, Menzies School of Health Research and Charles Darwin University, Darwin, Australia.
authors.forename: Rossarin
authors.initials: R
authors.lastname: Suwanarusk
authors.forename: Bruce
authors.initials: B
authors.lastname: Russell
authors.forename: Marina
authors.initials: M
authors.lastname: Chavchich
authors.forename: Ferryanto
authors.initials: F
authors.lastname: Chalfein
authors.forename: Enny
authors.initials: E
authors.lastname: Kenangalem
authors.forename: Varakorn
authors.initials: V
authors.lastname: Kosaisavee
authors.forename: Budi
authors.initials: B
authors.lastname: Prasetyorini
authors.forename: Kim A
authors.initials: KA
authors.lastname: Piera
authors.forename: Marion
authors.initials: M
authors.lastname: Barends
authors.forename: Alan
authors.initials: A
authors.lastname: Brockman
authors.forename: Usa
authors.initials: U
authors.lastname: Lek-Uthai
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Anstey
authors.forename: Emiliana
authors.initials: E
authors.lastname: Tjitra
authors.forename: François
authors.initials: F
authors.lastname: Nosten
authors.forename: Qin
authors.initials: Q
authors.lastname: Cheng
authors.forename: Ric N
authors.initials: RN
authors.lastname: Price
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D002738:Chloroquine / Q000494:pharmacology*; D004351:Drug Resistance; D014644:Genetic Variation; D006801:Humans; D007214:Indonesia; D020128:Inhibitory Concentration 50; D016780:Malaria, Vivax / Q000469:parasitology*; D008954:Models, Biological; D021261:Parasitic Sensitivity Tests; D010966:Plasmodium vivax / Q000378:metabolism*; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D015800:Protozoan Proteins / Q000737:chemistry
chemical_list: D000962:Antimalarials; D015800:Protozoan Proteins; D002738:Chloroquine