title: Marked variation in MSP-119 antibody responses to malaria in western Kenyan highlands.
abstract: BACKGROUND
  Assessment of malaria endemicity at different altitudes and transmission intensities, in the era of dwindling vector densities in the highlands, will provide valuable information for malaria control and surveillance. Measurement of serum anti-malarial antibodies is a useful marker of malaria exposure that indicates long-term transmission potential. We studied the serologic evidence of malaria endemicity at two highland sites along a transmission intensity cline. An improved understanding of the micro-geographic variation in malaria exposure in the highland ecosystems will be relevant in planning effective malaria control.
  
  
  METHODS
  Total IgG levels to Plasmodium falciparum MSP-119 were measured in an age-stratified cohort (< 5, 5-14 and ≥ 15 years) in 795 participants from an uphill and valley bottom residents during low and high malaria transmission seasons. Antibody prevalence and level was compared between different localities. Regression analysis was performed to examine the association between antibody prevalence and parasite prevalence. Age-specific MSP-119 seroprevalence data was fitted to a simple reversible catalytic model to investigate the relationship between parasite exposure and age.
  
  
  RESULTS
  Higher MSP-119 seroprevalence and density were observed in the valley residents than in the uphill dwellers. Adults (> 15 years) recorded high and stable immune response in spite of changing seasons. Lower responses were observed in children (≤ 15 years), which, fluctuated with changing seasons particularly in the valley residents. In the uphill population, annual seroconversion rate (SCR) was 8.3% and reversion rate was 3.0%, with seroprevalence reaching a plateau of 73.3% by age of 20. Contrary, in the valley bottom population, the annual SCR was 35.8% and the annual seroreversion rate was 3.5%, and seroprevalence in the population had reached 91.2% by age 10.
  
  
  CONCLUSIONS
  The study reveals the micro-geographic variation in malaria endemicity in the highland eco-system; this validates the usefulness of sero-epidemiological tools in assessing malaria endemicity in the era of decreasing sensitivity of conventional tools.
authors.affiliation: Center for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya. kingsleybadu@yahoo.com
authors.forename: Kingsley
authors.initials: K
authors.lastname: Badu
authors.forename: Yaw Asare
authors.initials: YA
authors.lastname: Afrane
authors.forename: John
authors.initials: J
authors.lastname: Larbi
authors.forename: Virginia Ann
authors.initials: VA
authors.lastname: Stewart
authors.forename: John
authors.initials: J
authors.lastname: Waitumbi
authors.forename: Evelina
authors.initials: E
authors.lastname: Angov
authors.forename: John M
authors.initials: JM
authors.lastname: Ong'echa
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Perkins
authors.forename: Guofa
authors.initials: G
authors.lastname: Zhou
authors.forename: Andrew
authors.initials: A
authors.lastname: Githeko
authors.forename: Guiyun
authors.initials: G
authors.lastname: Yan
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D019353:Endemic Diseases; D005260:Female; D005843:Geography; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007223:Infant; D007630:Kenya / Q000453:epidemiology; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000276:immunology*; D008297:Male; D020066:Merozoite Surface Protein 1 / Q000276:immunology*; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000276:immunology*; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D000913:Antibodies, Protozoan; D007074:Immunoglobulin G; D020066:Merozoite Surface Protein 1