Detecting Foci of Malaria Transmission with School Surveys: A Pilot Study in the Gambia

Abstract

BackgroundIn areas of declining malaria transmission such as in The Gambia, the identification of malaria infected individuals becomes increasingly harder. School surveys may be used to identify foci of malaria transmission in the community.MethodsThe survey was carried out in May–June 2011, before the beginning of the malaria transmission season. Thirty two schools in the Upper River Region of The Gambia were selected with probability proportional to size; in each school approximately 100 children were randomly chosen for inclusion in the study. Each child had a finger prick blood sample collected for the determination of antimalarial antibodies by ELISA, malaria infection by microscopy and PCR, and for haemoglobin measurement. In addition, a simple questionnaire on socio-demographic variables and the use of insecticide-treated bed nets was completed. The cut-off for positivity for antimalarial antibodies was obtained using finite mixture models. The clustered nature of the data was taken into account in the analyses.ResultsA total of 3,277 children were included in the survey. The mean age was 10 years (SD = 2.7) [range 4–21], with males and females evenly distributed. The prevalence of malaria infection as determined by PCR was 13.6% (426/3124) [95% CI = 12.2–16.3] with marked variation between schools (range 3–25%, p<0.001), while the seroprevalence was 7.8% (234/2994) [95%CI = 6.4–9.8] for MSP119, 11.6% (364/2997) [95%CI = 9.4–14.5] for MSP2, and 20.0% (593/2973) [95% CI = 16.5–23.2) for AMA1. The prevalence of all the three antimalarial antibodies positive was 2.7% (79/2920).ConclusionsThis survey shows that malaria prevalence and seroprevalence before the transmission season were highly heterogeneous.

School-Based Countrywide Seroprevalence Survey Reveals Spatial Heterogeneity in Malaria Transmission in the Gambia

“…From the microscopy results, the prevalence of infection was zero in several schools and not very high in all other schools. The schools with distinctly notable prevalence are located towards the eastern border of the country and the values reported are similar to those from earlier surveys in the area [10] , [14] and suggest that transmission in the eastern part, compared to the rest of the country, may be relatively unchanged or is declining at a much slower rate.…”

“…This is probably the most extensive description of the burden of malaria infection in The Gambia at the end of the dry season when malaria transmission has practically ceased and supports the evidence for heterogeneity and declining transmission across the country [10] , [14] , [18] . Asymptomatic malaria infections are common, persistent but yet difficult to measure [19] .…”

“…Antibodies against merozoite surface protein-1 19 (MSP1 19 ) were determined by indirect ELISA with samples eluted from collected filter papers using previously published methods [14] .…”

“…In this context, school-based serological surveys may be an effective and operationally attractive alternative to population-based surveys for identifying areas with varying transmission [13] . A pilot survey of 32 schools in the Upper River Region; one of the six administrative regions of The Gambia, showed that transmission in the area was quite heterogeneous and identified potential foci of transmission [14] .…”

Location, location, location: environmental factors better predict malaria-positive individuals during reactive case detection than index case demographics in Southern Province, Zambia

“…Identifying and clearing these pockets is key for malaria elimination programmes to succeed [2]. Population-based surveys of malaria parasite prevalence have been employed to find clusters of transmission, e.g., in Sudan [3], while school-based surveys have also been trialled in The Gambia [4]. Unfortunately, as transmission drops to low levels the utility of these population-based surveys for identifying residual transmission rapidly declines.…”