title: Comparison of PfHRP-2/pLDH ELISA, qPCR and microscopy for the detection of plasmodium events and prediction of sick visits during a malaria vaccine study.
abstract: BACKGROUND
  Compared to expert malaria microscopy, malaria biomarkers such as Plasmodium falciparum histidine rich protein-2 (PfHRP-2), and PCR provide superior analytical sensitivity and specificity for quantifying malaria parasites infections. This study reports on parasite prevalence, sick visits parasite density and species composition by different diagnostic methods during a phase-I malaria vaccine trial.
  
  
  METHODS
  Blood samples for microscopy, PfHRP-2 and Plasmodium lactate dehydrogenase (pLDH) ELISAs and real time quantitative PCR (qPCR) were collected during scheduled (n = 298) or sick visits (n = 38) from 30 adults participating in a 112-day vaccine trial. The four methods were used to assess parasite prevalence, as well as parasite density over a 42-day period for patients with clinical episodes.
  
  
  RESULTS
  During scheduled visits, qPCR (39.9%, N = 119) and PfHRP-2 ELISA (36.9%, N = 110) detected higher parasite prevalence than pLDH ELISA (16.8%, N = 50) and all methods were more sensitive than microscopy (13.4%, N = 40). All microscopically detected infections contained P. falciparum, as mono-infections (95%) or with P. malariae (5%). By qPCR, 102/119 infections were speciated. P. falciparum predominated either as monoinfections (71.6%), with P. malariae (8.8%), P. ovale (4.9%) or both (3.9%). P. malariae (6.9%) and P. ovale (1.0%) also occurred as co-infections (2.9%). As expected, higher prevalences were detected during sick visits, with prevalences of 65.8% (qPCR), 60.5% (PfHRP-2 ELISA), 21.1% (pLDH ELISA) and 31.6% (microscopy). PfHRP-2 showed biomass build-up that climaxed (1813±3410 ng/mL SD) at clinical episodes.
  
  
  CONCLUSIONS
  PfHRP-2 ELISA and qPCR may be needed for accurately quantifying the malaria parasite burden. In addition, qPCR improves parasite speciation, whilst PfHRP-2 ELISA is a potential predictor for clinical disease caused by P. falciparum.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00666380.
authors.affiliation: Walter Reed Project, Kenya Medical Research Institute, Kisumu, Kenya.
authors.forename: Ismail Mahat
authors.initials: IM
authors.lastname: Bashir
authors.forename: Nekoye
authors.initials: N
authors.lastname: Otsyula
authors.forename: George
authors.initials: G
authors.lastname: Awinda
authors.forename: Michele
authors.initials: M
authors.lastname: Spring
authors.forename: Petra
authors.initials: P
authors.lastname: Schneider
authors.forename: John Njenga
authors.initials: JN
authors.lastname: Waitumbi
mesh_terms: D000293:Adolescent; D000328:Adult; D000953:Antigens, Protozoan / Q000097:blood* / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005260:Female; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000097:blood* / Q000235:genetics; D017780:Malaria Vaccines / Q000008:administration & dosage*; D016778:Malaria, Falciparum / Q000097:blood* / Q000276:immunology / Q000517:prevention & control; D008297:Male; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000166:cytology / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D010965:Plasmodium malariae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000097:blood* / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D000953:Antigens, Protozoan; C514457:HRP-2 antigen, Plasmodium falciparum; D017780:Malaria Vaccines; D015800:Protozoan Proteins; D007770:L-Lactate Dehydrogenase
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