title: Geographical patterns of malaria transmission based on serological markers for falciparum and vivax malaria in Ratanakiri, Cambodia.
abstract: BACKGROUND
  Malaria transmission is highly heterogeneous, especially in low endemic countries, such as Cambodia. This results in geographical clusters of residual transmission in the dry, low transmission season, which can fuel the transmission to wider areas or populations during the wet season. A better understanding of spatial clustering of malaria can lead to a more efficient, targeted strategy to reduce malaria transmission. This study aims to evaluate the potential of the use of serological markers to define spatial patterns in malaria exposure.
  
  
  METHODS
  Blood samples collected in a community-based randomized trial performed in 98 high endemic communities in Ratanakiri province, north-eastern Cambodia, were screened with a multiplex serological assay for five serological markers (three Plasmodium falciparum and two Plasmodium vivax). The antibody half-lives range from approximately six months until more than two years. Geographical heterogeneity in malaria transmission was examined using a spatial scan statistic on serology, PCR prevalence and malaria incidence rate data. Furthermore, to identify behavioural patterns or intrinsic factors associated with malaria exposure (antibody levels), risk factor analyses were performed by using multivariable random effect logistic regression models. The serological outcomes were then compared to PCR prevalence and malaria incidence data.
  
  
  RESULTS
  A total of 6502 samples from two surveys were screened in an area where the average parasite prevalence estimated by PCR among the selected villages is 3.4 %. High-risk malaria pockets were observed adjacent to the 'Tonle San River' and neighbouring Vietnam for all three sets of data (serology, PCR prevalence and malaria incidence rates). The main risk factors for all P. falciparum antigens and P. vivax MSP1.19 are age, ethnicity and staying overnight at the plot hut.
  
  
  CONCLUSIONS
  It is possible to identify similar malaria pockets of higher malaria transmission together with the potential risk factors by using serology instead of PCR prevalence or malaria incidence data. In north-eastern Cambodia, the serological markers show that malaria transmission occurs mainly in adults staying overnight in plot huts in the field. Pf.GLURP.R2 showed a shrinking pocket of malaria transmission over time, and Pf.MSP1.19, CSP, PvAMA1 were also informative for current infection to a lesser extent. Therefore, serology could contribute in future research. However, further in-depth research in selecting the best combination of antigens is required.
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium. kkerkhof@itg.be.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium. kkerkhof@itg.be.
authors.forename: Karen
authors.identifier: http://orcid.org/0000-0002-2208-9902
authors.initials: K
authors.lastname: Kerkhof
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biology, University of Antwerp, Antwerp, Belgium.
authors.forename: Vincent
authors.initials: V
authors.lastname: Sluydts
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
authors.forename: Somony
authors.initials: S
authors.lastname: Heng
authors.affiliation: Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
authors.forename: Saorin
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
authors.forename: Myrthe
authors.initials: M
authors.lastname: Pareyn
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Laura
authors.initials: L
authors.lastname: Willen
authors.affiliation: Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
authors.forename: Lydie
authors.initials: L
authors.lastname: Canier
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
authors.forename: Siv
authors.initials: S
authors.lastname: Sovannaroth
authors.affiliation: Molecular Epidemiology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia.
authors.forename: Didier
authors.initials: D
authors.lastname: Ménard
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia.
authors.forename: Tho
authors.initials: T
authors.lastname: Sochantha
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.|Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
authors.forename: Marc
authors.initials: M
authors.lastname: Coosemans
authors.affiliation: Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Lies
authors.initials: L
authors.lastname: Durnez
mesh_terms: D000293:Adolescent; D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood*; D002160:Cambodia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D018562:Disease Transmission, Infectious; D005260:Female; D006801:Humans; D015994:Incidence; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000635:transmission*; D016780:Malaria, Vivax / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000276:immunology; D010966:Plasmodium vivax / Q000276:immunology; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012698:Serologic Tests; D019371:Topography, Medical; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan
keywords: Cambodia; Geographical patterns; Heterogeneous transmission; Malaria; Malaria pockets; Serological markers