title: The shape of the iceberg: quantification of submicroscopic Plasmodium falciparum and Plasmodium vivax parasitaemia and gametocytaemia in five low endemic settings in Ethiopia.
abstract: The widespread presence of low-density asymptomatic infections with concurrent gametocytes may be a stumbling block for malaria elimination. This study investigated the asymptomatic reservoir of Plasmodium falciparum and Plasmodium vivax infections in schoolchildren from five settings in northwest Ethiopia.
  
  
  
  Two cross-sectional surveys were conducted in June and November 2015, enrolling 551 students from five schools and 294 students from three schools, respectively. Finger prick whole blood and plasma samples were collected. The prevalence and density of P. falciparum and P. vivax parasitaemia and gametocytaemia were determined by 18S rRNA quantitative PCR (qPCR) and pfs25 and pvs25 reverse transcriptase qPCR. Antibodies against blood stage antigens apical membrane antigen-1 (AMA-1) and merozoite surface protein-1 (MSP-119) were measured for both species.
  
  
  
  Whilst only 6 infections were detected by microscopy in 881 slides (0.7%), 107 of 845 blood samples (12.7%) were parasite positive by (DNA-based) qPCR. qPCR parasite prevalence between sites and surveys ranged from 3.8 to 19.0% for P. falciparum and 0.0 to 9.0% for P. vivax. The median density of P. falciparum infections (n = 85) was 24.4 parasites/µL (IQR 18.0-34.0) and the median density of P. vivax infections (n = 28) was 16.4 parasites/µL (IQR 8.8-55.1). Gametocyte densities by (mRNA-based) qRT-PCR were strongly associated with total parasite densities for both P. falciparum (correlation coefficient = 0.83, p = 0.010) and P. vivax (correlation coefficient = 0.58, p = 0.010). Antibody titers against P. falciparum AMA-1 and MSP-119were higher in individuals who were P. falciparum parasite positive in both surveys (p < 0.001 for both comparisons).
  
  
  
  This study adds to the available evidence on the wide-scale presence of submicroscopic parasitaemia by quantifying submicroscopic parasite densities and concurrent gametocyte densities. There was considerable heterogeneity in the occurrence of P. falciparum and P. vivax infections and serological markers of parasite exposure between the examined low endemic settings in Ethiopia.
authors.affiliation: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.|Medical Biotechnology Unit, Institute of Biotechnology, Addis Ababa University, Addis Ababa, Ethiopia.|Armauer Hansen Research Institute (AHRI), Addis Ababa, Ethiopia.
authors.forename: Fitsum G
authors.identifier: 0000-0003-1931-1442
authors.initials: FG
authors.lastname: Tadesse
authors.affiliation: Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Lotus
authors.initials: L
authors.lastname: van den Hoogen
authors.affiliation: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Kjerstin
authors.initials: K
authors.lastname: Lanke
authors.affiliation: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Jodie
authors.initials: J
authors.lastname: Schildkraut
authors.affiliation: Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Kevin
authors.initials: K
authors.lastname: Tetteh
authors.affiliation: Armauer Hansen Research Institute (AHRI), Addis Ababa, Ethiopia.
authors.forename: Abraham
authors.initials: A
authors.lastname: Aseffa
authors.affiliation: Department of Microbial, Cellular and Molecular Biology, College of Natural Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
authors.forename: Hassen
authors.initials: H
authors.lastname: Mamo
authors.affiliation: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Sauerwein
authors.affiliation: Swiss Tropical and Public Health Institute, Basel, Switzerland.|University of Basel, Basel, Switzerland.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Felger
authors.affiliation: Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Drakeley
authors.affiliation: Armauer Hansen Research Institute (AHRI), Addis Ababa, Ethiopia.
authors.forename: Endalamaw
authors.initials: E
authors.lastname: Gadissa
authors.affiliation: Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands. teun.bousema@radboudumc.nl.|Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, UK. teun.bousema@radboudumc.nl.
authors.forename: Teun
authors.initials: T
authors.lastname: Bousema
mesh_terms: D000293:Adolescent; D058345:Asymptomatic Infections / Q000453:epidemiology; D002648:Child; D003430:Cross-Sectional Studies; D019353:Endemic Diseases / Q000706:statistics & numerical data*; D005002:Ethiopia / Q000453:epidemiology; D005260:Female; D006801:Humans; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000469:parasitology; D016780:Malaria, Vivax / Q000453:epidemiology* / Q000469:parasitology; D008297:Male; D018512:Parasitemia / Q000453:epidemiology* / Q000469:parasitology; D010963:Plasmodium falciparum / Q000235:genetics / Q000302:isolation & purification; D010966:Plasmodium vivax / Q000235:genetics / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012337:RNA, Ribosomal, 18S / Q000235:genetics
chemical_list: D012337:RNA, Ribosomal, 18S
keywords: Asymptomatic; El Ǹino; Elimination; PCR; School; Serology; Submicroscopic; Transmission