title: Persistent Plasmodium falciparum and Plasmodium vivax infections in a western Cambodian population: implications for prevention, treatment and elimination strategies.
abstract: BACKGROUND
  Subclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, particularly in low transmission areas.
  
  
  METHODS
  Using ultrasensitive quantitative PCR (uPCR) for the detection of parasitaemia, the entire population of three Cambodian villages in Pailin province were followed for 1 year at three-monthly intervals. A cohort of adult participants found initially to have asymptomatic malaria parasitaemia was followed monthly over the same period.
  
  
  RESULTS
  The initial cross sectional survey in June 2013 (M0) of 1447 asymptomatic residents found that 32 (2.2%) had Plasmodium falciparum, 48 (3.3%) had P. vivax, 4 (0.3%) had mixed infections and in 142/1447 (9.8%) malaria was detected but there was insufficient DNA to identify the species (Plasmodium. species). Polymorphisms in the 'K13-propeller' associated with reduced susceptibility to artemisinin derivatives (C580Y) were found in 17/32 (51%) P. falciparum strains. Monthly follow-up without treatment of 24 adult participants with asymptomatic mono or mixed P. falciparum infections found that 3/24 (13%) remained parasitaemic for 2-4 months, whereas the remaining 21/24 (87%) participants had cleared their parasitaemia after 1 month. In contrast, 12/34 (35%) adult participants with P. vivax mono-infection at M0 had malaria parasites (P. vivax or P. sp.) during four or more of the following 11 monthly surveys.
  
  
  CONCLUSIONS
  This longitudinal survey in a low transmission setting shows limited duration of P. falciparum carriage, but prolonged carriage of P. vivax infections. Radical treatment of P. vivax infections by 8-aminoquinoline regimens may be required to eliminate all malaria from Cambodia. Trial registration ClinicalTrials.gov NCT01872702.
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. Rupam@tropmedres.ac.
authors.forename: Rupam
authors.initials: R
authors.lastname: Tripura
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Peto
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Chalk
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
authors.forename: Sue J
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Pasathorn
authors.initials: P
authors.lastname: Sirithiranont
authors.affiliation: National Centre for Parasitology, Entomology, and Malaria Control (CNM), Trapeng Svay Village, Sangkat Phnom Penh Thmei, Khan Sen Sok, Phnom Penh, Cambodia.
authors.forename: Chea
authors.initials: C
authors.lastname: Nguon
authors.affiliation: WorldWide Antimalarial Resistance Network, Asia Regional Centre, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Mehul
authors.initials: M
authors.lastname: Dhorda
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.|Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, 02115, USA.
authors.forename: Lorenz
authors.initials: L
authors.lastname: von Seidlein
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.|Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, 02115, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Maude
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
authors.forename: Nicholas P J
authors.initials: NP
authors.lastname: Day
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Mallika
authors.initials: M
authors.lastname: Imwong
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: White
authors.affiliation: Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.|Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
authors.forename: Arjen M
authors.initials: AM
authors.lastname: Dondorp
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D058345:Asymptomatic Infections / Q000453:epidemiology; D002160:Cambodia / Q000453:epidemiology; D002353:Carrier State / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D062665:Epidemiological Monitoring; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D016778:Malaria, Falciparum / Q000453:epidemiology*; D016780:Malaria, Vivax / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D018512:Parasitemia / Q000175:diagnosis / Q000453:epidemiology; D060888:Real-Time Polymerase Chain Reaction; D012424:Rural Population; D055815:Young Adult
keywords: Artemisinins; Cambodia; Clearance; Cohort; Falciparum; Malaria; PCR; Pailin; Persistence; Plasmodium; Resistance; Vivax