Serological evidence of vector and parasite exposure in Southern Ghana: the dynamics of malaria transmission intensity.

Kingsley Badu,Kingsley Badu,Ben Gyan,Ben Gyan,Kwadwo Ansah Koram,Kwadwo Ansah Koram,Daniel Dodoo,Daniel Dodoo,Chris Drakeley,Maxwell Appawu,Maxwell Appawu,Ellis Owusu-Dabo,Ellis Owusu-Dabo,Daniel Mensah,Guiyun Yan,Guofa Zhou

doi:10.1186/s13071-015-0861-y

Abstract

BackgroundSeroepidemiology provides robust estimates for tracking malaria transmission when intensity is low and useful when there is no baseline entomological data. Serological evidence of exposure to malaria vectors and parasite contribute to our understanding of the risk of pathogen transmission, and facilitates implementation of targeted interventions. Ab to Anopheles gambiae salivary peptide (gSG6-P1) and merozoite surface protein one (MSP-119) reflect human exposure to malaria vectors and parasites. This study estimated malaria transmission dynamics using serological evidence of vector and parasite exposure in southern Ghana.MethodsTotal IgG responses to both antigens in an age stratified cohort (<5, 5–14, >14) were measured from South-eastern Ghana. 295 randomly selected sera were analyzed from archived samples belonging to a cohort study that were followed at 3 consecutive survey months (n = 885); February, May and August 2009. Temporal variations in seroprevalence of both antigens as well as differences between the age-stratified cohorts were determined by χ2 test with p < 0.05 statistically significant. Non-parametric repeated ANOVA – Friedman’s test was used to test differences in antibody levels. Seroprevalence data were fitted to reversible catalytic model to estimate sero-conversion rates.ResultsWhereas parasite prevalence was generally low 2.4%, 2.7% and 2.4% with no apparent trends with season, seroprevalence to both gSG6-P1 and MSP119 were high (59%, 50.9%, 52.2%) and 57.6%, 52.3% and 43.6% in respective order from Feb. to August. Repeated measures ANOVA showed differences in median antibody levels across surveys with specific significant differences between February and May but not August by post hoc Dunn’s multiple comparison tests for gSG6-P1. For MSP119, no differences were observed in antibody levels between February and May but a significant decline was observed from May to August. Seroconversion rates for gSG6-P1 increased by 1.5 folds from February to August and 3 folds for MSP119.ConclusionData suggests exposure to infectious bites may be declining whereas mosquito bites remains high. Sustained malaria control efforts and surveillance are needed to drive malaria further down and to prevent catastrophic rebound. Operational factors for scaling up have been discussed.

Highlights

Seroepidemiology provides robust estimates for tracking malaria transmission when intensity is low and useful when there is no baseline entomological data
Study population and parasite prevalence A total of 295 subjects had data available for all the 3 surveys (Feb, May and Aug) and all analysis were based on the 295 selected samples. 27% out of the subjects were less than 5 yrs whilst the majority of the study subjects were between the ages of 5 and 14
Parasite prevalence and antigen specific seroprevalence Parasite prevalence was generally low with no particular seasonal trends observed across the three contact months (Table 1)

Summary

Introduction

Seroepidemiology provides robust estimates for tracking malaria transmission when intensity is low and useful when there is no baseline entomological data. The intrinsic uncertainty in measuring Ma with methods such as human landing catches, resting collections, pyrethrum spray catches, and Centers for Disease Control and Prevention (CDC) light traps are all subject to operator-related variability, such that results may not be reproducible or accurately reflective of the overall local population, and the need for standardized methods for measuring both Ma and SR [8,9] limit the precision and accuracy of EIR and its potential for measuring a change in transmission This is especially so at low transmission intensities, where it is difficult to catch sufficient mosquitoes. The limitations associated with measuring malaria transmission by vector mosquitoes are expected to become even more pronounced as ongoing implementation of available control methods, including indoor residual spraying (IRS) and insecticide-treated nets (ITNs), drive down mosquito and malaria endemicity levels [10]

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Discussion

Conclusion