title: Examining Plasmodium falciparum and P. vivax clearance subsequent to antimalarial drug treatment in the Myanmar-China border area based on quantitative real-time polymerase chain reaction.
abstract: BACKGROUND
  Recent emergence of artemisinin-resistant P. falciparum has posed a serious hindrance to the elimination of malaria in the Greater Mekong Subregion. Parasite clearance time, a measure of change in peripheral parasitaemia in a sequence of samples taken after treatment, can be used to reflect the susceptibility of parasites or the efficiency of antimalarials. The association of genetic polymorphisms and artemisinin resistance has been documented. This study aims to examine clearance time of P. falciparum and P. vivax parasitemia as well as putative gene mutations associated with residual or recurred parasitemia in Myanmar.
  
  
  METHODS
  A total of 63 P. falciparum and 130 P. vivax samples collected from two internally-displaced populations and one surrounding village were examined for parasitemia changes. At least four samples were taken from each patient, at the first day of diagnosis up to 3 months following the initial treatment. The amount of parasite gene copy number was estimated using quantitative real-time PCR based on a species-specific region of the 18S rRNA gene. For samples that showed residual or recurred parasitemia after treatment, microsatellites were used to identify the 'post-treatment' parasite genotype and compared such with the 'pre-treatment' genotype. Mutations in genes pfcrt, pfmdr1, pfatp6, pfmrp1 and pfK13 that are potentially associated with ACT resistance were examined to identify if mutation is a factor for residual or persistent parasitemia.
  
  
  RESULTS
  Over 30% of the P. falciprium infections showed delayed clearance of parasitemia after 2-3 days of treatment and 9.5% showed recurred parasitemia. Mutations in codon 876 of the pfmrp1 corroborated significance association with slow clearance time. However, no association was observed in the variation in pfmdr1 gene copy number as well as mutations of various codonsinpfatp6, pfcrt, and pfK13 with clearance time. For P. vivax, over 95% of the infections indicated cleared parasitemia at days 2-3 of treatment. Four samples were found to be re-infected with new parasite strains based on microsatellite genotypes after initial treatment.
  
  
  CONCLUSIONS
  The appearance of P.falciparum infected samples showing delayed clearance or recurred parasitemia after treatment raises concerns on current treatment and ACT drug resistance.
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Lo
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nguyen
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA.
authors.forename: Winny
authors.initials: W
authors.lastname: Oo
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hemming-Schroeder
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA.
authors.forename: Guofa
authors.initials: G
authors.lastname: Zhou
authors.affiliation: Department of Pathogen Biology and Immunology, Kunming Medical University, Kunming, China.
authors.forename: Zhaoqing
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Department of Entomology, Pennsylvania State University, University Park, PA, USA.
authors.forename: Liwang
authors.initials: L
authors.lastname: Cui
authors.affiliation: Program in Public Health, University of California at Irvine, Irvine, CA, 92697-4050, USA. guiyuny@uci.edu.
authors.forename: Guiyun
authors.initials: G
authors.lastname: Yan
mesh_terms: D000962:Antimalarials / Q000494:pharmacology / Q000627:therapeutic use*; D037621:Artemisinins / Q000494:pharmacology; D002681:China; D016054:DNA, Protozoan / Q000032:analysis / Q000378:metabolism; D004351:Drug Resistance / Q000235:genetics; D005838:Genotype; D006801:Humans; D016778:Malaria, Falciparum / Q000175:diagnosis* / Q000188:drug therapy*; D016780:Malaria, Vivax / Q000188:drug therapy* / Q000469:parasitology; D018895:Microsatellite Repeats / Q000235:genetics; D002052:Myanmar; 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; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D000962:Antimalarials; D037621:Artemisinins; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C031327:artemisinin
keywords: Artemisinin-combined therapy; Malaria; Microsatellite; P. falciparum; P. vivax; Parasite clearance; Quantitative PCR; Resistance genes