Factors associated with high heterogeneity of malaria at fine spatial scale in the Western Kenyan highlands.
The East African highlands are fringe regions between stable and unstable malaria transmission. What factors contribute to the heterogeneity of malaria exposure on different spatial scales within larger foci has not been extensively studied. In a comprehensive, community-based cross-sectional survey an attempt was made to identify factors that drive the macro- and micro epidemiology of malaria in a fringe region using parasitological and serological outcomes.



A large cross-sectional survey including 17,503 individuals was conducted across all age groups in a 100 km(2) area in the Western Kenyan highlands of Rachuonyo South district. Households were geo-located and prevalence of malaria parasites and malaria-specific antibodies were determined by PCR and ELISA. Household and individual risk-factors were recorded. Geographical characteristics of the study area were digitally derived using high-resolution satellite images.



Malaria antibody prevalence strongly related to altitude (1350-1600 m, p < 0.001). A strong negative association with increasing altitude and PCR parasite prevalence was found. Parasite carriage was detected at all altitudes and in all age groups; 93.2 % (2481/2663) of malaria infections were apparently asymptomatic. Malaria parasite prevalence was associated with age, bed net use, house construction features, altitude and topographical wetness index. Antibody prevalence was associated with all these factors and distance to the nearest water body.



Altitude was a major driver of malaria transmission in this study area, even across narrow altitude bands. The large proportion of asymptomatic parasite carriers at all altitudes and the age-dependent acquisition of malaria antibodies indicate stable malaria transmission; the strong correlation between current parasite carriage and serological markers of malaria exposure indicate temporal stability of spatially heterogeneous transmission.
Department of Medical Microbiology, Radboud University Medical Centre, Geert Grooteplein 26-28, 6525, GA, Nijmegen, The Netherlands.|European Programme for Public Health Microbiology Training, European Centre of Disease Prevention and Control (ECDC), Stockholm, Sweden.
Amrish Y
AY
Baidjoe
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK.|Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD, 21205, USA.
Jennifer
J
Stevenson
Department of Mathematical Sciences, University of Bath, Claverton Down, Bath, BA2 7AY, UK.
Philip
P
Knight
Department of Medical Microbiology, Radboud University Medical Centre, Geert Grooteplein 26-28, 6525, GA, Nijmegen, The Netherlands.
William
W
Stone
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK.
Gillian
G
Stresman
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Victor
V
Osoti
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Euniah
E
Makori
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Chrispin
C
Owaga
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Wycliffe
W
Odongo
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Pauline
P
China
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Shehu
S
Shagari
Kenya Medical Research Institute, Mumias Road, Kisumu Station, Kisian, Kisumu, Kenya.
Simon
S
Kariuki
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK.
Chris
C
Drakeley
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK.
Jonathan
J
Cox
Department of Medical Microbiology, Radboud University Medical Centre, Geert Grooteplein 26-28, 6525, GA, Nijmegen, The Netherlands. teun.bousema@lshtm.ac.uk.|Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK. teun.bousema@lshtm.ac.uk.
Teun
T
Bousema
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000531:Altitude; D000913:Antibodies, Protozoan / Q000097:blood; D058070:Asymptomatic Diseases / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D016054:DNA, Protozoan / Q000235:genetics; D018562:Disease Transmission, Infectious; D004797:Enzyme-Linked Immunosorbent Assay; D005191:Family Characteristics; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007630:Kenya / Q000453:epidemiology; D008288:Malaria / Q000453:epidemiology* / Q000635:transmission; D008297:Male; D008875:Middle Aged; D010961:Plasmodium / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012307:Risk Factors; D062206:Spatial Analysis; D019371:Topography, Medical; D055815:Young Adult
D000913:Antibodies, Protozoan; D016054:DNA, Protozoan
Elimination; Heterogeneity; Hotspots; Malaria; Plasmodium falciparum; Polymerase chain reaction; Risk-factors; Serology; Transmission