title: Diagnostic performance of a novel loop-mediated isothermal amplification (LAMP) assay targeting the apicoplast genome for malaria diagnosis in a field setting in sub-Saharan Africa.
abstract: BACKGROUND
  New diagnostic tools to detect reliably and rapidly asymptomatic and low-density malaria infections are needed as their treatment could interrupt transmission. Isothermal amplification techniques are being explored for field diagnosis of malaria. In this study, a novel molecular tool (loop-mediated isothermal amplification-LAMP) targeting the apicoplast genome of Plasmodium falciparum was evaluated for the detection of asymptomatic malaria-infected individuals in a rural setting in The Gambia.
  
  
  METHODS
  A blood was collected from 341 subjects (median age 9 years, range 1-68 years) screened for malaria. On site, a rapid diagnostic test (RDT, SD Bioline Malaria Antigen P.f) was performed, thick blood films (TBF) slides for microscopy were prepared and dry blood spots (DBS) were collected on Whatman(®) 903 Specimen collection paper. The TBF and DBS were transported to the field laboratory where microscopy and LAMP testing were performed. The latter was done on DNA extracted from the DBS using a crude (methanol/heating) extraction method. A laboratory-based PCR amplification was done on all the samples using DNA extracted with the Qiagen kit and its results were taken as reference for all the other tests.
  
  
  RESULTS
  Plasmodium falciparum malaria prevalence was 37 % (127/341) as detected by LAMP, 30 % (104/341) by microscopy and 37 % (126/341) by RDT. Compared to the reference PCR method, sensitivity was 92 % for LAMP, 78 % for microscopy, and 76 % for RDT; specificity was 97 % for LAMP, 99 % for microscopy, and 88 % for RDT. Area under the receiver operating characteristic (ROC) curve in comparison with the reference standard was 0.94 for LAMP, 0.88 for microscopy and 0.81 for RDT. Turn-around time for the entire LAMP assay was approximately 3 h and 30 min for an average of 27 ± 9.5 samples collected per day, compared to a minimum of 10 samples an hour per operator by RDT and over 8 h by microscopy.
  
  
  CONCLUSIONS
  The LAMP assay could produce reliable results the same day of the screening. It could detect a higher proportion of low density malaria infections than the other methods tested and may be used for large campaigns of systematic screening and treatment.
authors.affiliation: Medical Research Council Unit, PO Box 273, Banjul, The Gambia. eoriero@mrc.gm.|Institute of Tropical Medicine, Antwerp, Belgium. eoriero@mrc.gm.|International Health Unit, University of Antwerp, Antwerp, Belgium. eoriero@mrc.gm.
authors.forename: Eniyou C
authors.initials: EC
authors.lastname: Oriero
authors.affiliation: Medical Research Council Unit, PO Box 273, Banjul, The Gambia. jokebe@mrc.gm.|Institute of Tropical Medicine, Antwerp, Belgium. jokebe@mrc.gm.|International Health Unit, University of Antwerp, Antwerp, Belgium. jokebe@mrc.gm.
authors.forename: Joseph
authors.initials: J
authors.lastname: Okebe
authors.affiliation: Institute of Tropical Medicine, Antwerp, Belgium. jjacobs@itg.be.|Department of Microbiology and Immunology, KU Leuven, Leuven, Belgium. jjacobs@itg.be.
authors.forename: Jan
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: International Health Unit, University of Antwerp, Antwerp, Belgium. jean-pierre.vangeertruyden@uantwerpen.be.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Van Geertruyden
authors.affiliation: Medical Research Council Unit, PO Box 273, Banjul, The Gambia. dnwakanma@mrc.gm.
authors.forename: Davis
authors.initials: D
authors.lastname: Nwakanma
authors.affiliation: Medical Research Council Unit, PO Box 273, Banjul, The Gambia. udalessandro@mrc.gm.|Institute of Tropical Medicine, Antwerp, Belgium. udalessandro@mrc.gm.|London School of Hygiene and Tropical Medicine, London, UK. udalessandro@mrc.gm.
authors.forename: Umberto
authors.initials: U
authors.lastname: D'Alessandro
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D063546:Apicoplasts / Q000235:genetics*; D001769:Blood / Q000469:parasitology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005714:Gambia; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D025202:Molecular Diagnostic Techniques / Q000379:methods*; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D010963:Plasmodium falciparum / Q000235:genetics / Q000302:isolation & purification*; D012424:Rural Population; D012680:Sensitivity and Specificity; D055815:Young Adult