title: Numerical Distributions of Parasite Densities During Asymptomatic Malaria.
abstract: BACKGROUND
  Asymptomatic parasitemia is common even in areas of low seasonal malaria transmission, but the true proportion of the population infected has not been estimated previously because of the limited sensitivity of available detection methods.
  
  
  METHODS
  Cross-sectional malaria surveys were conducted in areas of low seasonal transmission along the border between eastern Myanmar and northwestern Thailand and in western Cambodia. DNA was quantitated by an ultrasensitive polymerase chain reaction (uPCR) assay (limit of accurate detection, 22 parasites/mL) to characterize parasite density distributions for Plasmodium falciparum and Plasmodium vivax, and the proportions of undetected infections were imputed.
  
  
  RESULTS
  The prevalence of asymptomatic malaria as determined by uPCR was 27.5% (1303 of 4740 people tested). Both P. vivax and P. falciparum density distributions were unimodal and log normal, with modal values well within the quantifiable range. The estimated proportions of all parasitemic individuals identified by uPCR were >70% among individuals infected with P. falciparum and >85% among those infected with P. vivax. Overall, 83% of infections were predicted to be P. vivax infections, 13% were predicted to be P. falciparum infections, and 4% were predicted to be mixed infections. Geometric mean parasite densities were similar; 5601 P. vivax parasites/mL and 5158 P. falciparum parasites/mL.
  
  
  CONCLUSIONS
  This uPCR method identified most infected individuals in malaria-endemic areas. Malaria parasitemia persists in humans at levels that optimize the probability of generating transmissible gametocyte densities without causing illness.
authors.affiliation: Mahidol Oxford Research Unit Department of Molecular Tropical Medicine and Genetics.
authors.forename: Mallika
authors.initials: M
authors.lastname: Imwong
authors.affiliation: Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford WWARN, Churchill Hospital, Oxford, United Kingdom.
authors.forename: Kasia
authors.initials: K
authors.lastname: Stepniewska
authors.affiliation: Mahidol Oxford Research Unit.
authors.forename: Rupam
authors.initials: R
authors.lastname: Tripura
authors.affiliation: Mahidol Oxford Research Unit.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Peto
authors.affiliation: Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand.
authors.forename: Khin Maung
authors.initials: KM
authors.lastname: Lwin
authors.affiliation: Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand.
authors.forename: Benchawan
authors.initials: B
authors.lastname: Vihokhern
authors.affiliation: Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand.
authors.forename: Klanarong
authors.initials: K
authors.lastname: Wongsaen
authors.affiliation: Mahidol Oxford Research Unit Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
authors.forename: Lorenz
authors.initials: L
authors.lastname: von Seidlein
authors.affiliation: WorldWide Antimalarial Resistance Network (WWARN).
authors.forename: Mehul
authors.initials: M
authors.lastname: Dhorda
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, UPMC UMRS CR7 Centre d'Immunologie et de Maladies Infectieuses-Paris, Institut National de la Santé et de la Recherche Medicale U1135-Centre National de la Recherche Scientifique ERL 8255, Paris, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Snounou
authors.affiliation: Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand.
authors.forename: Lilly
authors.initials: L
authors.lastname: Keereecharoen
authors.affiliation: Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University, Bangkok.
authors.forename: Pratap
authors.initials: P
authors.lastname: Singhasivanon
authors.affiliation: Mahidol Oxford Research Unit.
authors.forename: Pasathorn
authors.initials: P
authors.lastname: Sirithiranont
authors.affiliation: Mahidol Oxford Research Unit.
authors.forename: Jem
authors.initials: J
authors.lastname: Chalk
authors.affiliation: National Center for Parasitology, Entomology, and Malaria Control, Phnom Penh, Cambodia.
authors.forename: Chea
authors.initials: C
authors.lastname: Nguon
authors.affiliation: Mahidol Oxford Research Unit Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
authors.forename: Nicholas P J
authors.initials: NP
authors.lastname: Day
authors.affiliation: Mahidol Oxford Research Unit Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
authors.forename: Francois
authors.initials: F
authors.lastname: Nosten
authors.affiliation: Mahidol Oxford Research Unit Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
authors.forename: Arjen
authors.initials: A
authors.lastname: Dondorp
authors.affiliation: Mahidol Oxford Research Unit Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: White
mesh_terms: D000293:Adolescent; D000328:Adult; D001210:Asia, Southeastern / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000469:parasitology*; D016780:Malaria, Vivax / Q000453:epidemiology* / Q000469:parasitology*; D008297:Male; D018512:Parasitemia / Q000453:epidemiology / Q000469:parasitology; D015995:Prevalence; D055815:Young Adult
keywords: PCR; Plasmodium falciparum; Plasmodium vivax; asymptomatic parasitemia; malaria