title: Sero-epidemiological evaluation of changes in Plasmodium falciparum and Plasmodium vivax transmission patterns over the rainy season in Cambodia.
abstract: BACKGROUND
  In Cambodia, malaria transmission is low and most cases occur in forested areas. Sero-epidemiological techniques can be used to identify both areas of ongoing transmission and high-risk groups to be targeted by control interventions. This study utilizes repeated cross-sectional data to assess the risk of being malaria sero-positive at two consecutive time points during the rainy season and investigates who is most likely to sero-convert over the transmission season.
  
  
  METHODS
  In 2005, two cross-sectional surveys, one in the middle and the other at the end of the malaria transmission season, were carried out in two ecologically distinct regions in Cambodia. Parasitological and serological data were collected in four districts. Antibodies to Plasmodium falciparum Glutamate Rich Protein (GLURP) and Plasmodium vivax Merozoite Surface Protein-1(19) (MSP-1(19)) were detected using Enzyme Linked Immunosorbent Assay (ELISA). The force of infection was estimated using a simple catalytic model fitted using maximum likelihood methods. Risks for sero-converting during the rainy season were analysed using the Classification and Regression Tree (CART) method.
  
  
  RESULTS
  A total of 804 individuals participating in both surveys were analysed. The overall parasite prevalence was low (4.6% and 2.0% for P. falciparum and 7.9% and 6.0% for P. vivax in August and November respectively). P. falciparum force of infection was higher in the eastern region and increased between August and November, whilst P. vivax force of infection was higher in the western region and remained similar in both surveys. In the western region, malaria transmission changed very little across the season (for both species). CART analysis for P. falciparum in the east highlighted age, ethnicity, village of residence and forest work as important predictors for malaria exposure during the rainy season. Adults were more likely to increase their antibody responses to P. falciparum during the transmission season than children, whilst members of the Charay ethnic group demonstrated the largest increases.
  
  
  CONCLUSIONS
  In areas of low transmission intensity, such as in Cambodia, the analysis of longitudinal serological data enables a sensitive evaluation of transmission dynamics. Consecutive serological surveys allow an insight into spatio-temporal patterns of malaria transmission. The use of CART enabled multiple interactions to be accounted for simultaneously and permitted risk factors for exposure to be clearly identified.
authors.affiliation: Institute of Tropical Medicine, Nationalestraat 155, Antwerp 2000, Belgium. jcook@itg.be
authors.forename: Jackie
authors.initials: J
authors.lastname: Cook
authors.forename: Nico
authors.initials: N
authors.lastname: Speybroeck
authors.forename: Tho
authors.initials: T
authors.lastname: Sochanta
authors.forename: Heng
authors.initials: H
authors.lastname: Somony
authors.forename: Mao
authors.initials: M
authors.lastname: Sokny
authors.forename: Filip
authors.initials: F
authors.lastname: Claes
authors.forename: Kristel
authors.initials: K
authors.lastname: Lemmens
authors.forename: Michael
authors.initials: M
authors.lastname: Theisen
authors.forename: Irene S
authors.initials: IS
authors.lastname: Soares
authors.forename: Umberto
authors.initials: U
authors.lastname: D'Alessandro
authors.forename: Marc
authors.initials: M
authors.lastname: Coosemans
authors.forename: Annette
authors.initials: A
authors.lastname: Erhart
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D002160:Cambodia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; 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; D012307:Risk Factors; D012621:Seasons; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan