Abstract
BackgroundIntermittent preventive antimalarial treatment in infants (IPTi) is currently evaluated as a malaria control strategy. Among the factors influencing the extent of protection that is provided by IPTi are the transmission intensity, seasonality, drug resistance patterns, and the schedule of IPTi administrations. The aim of this study was to determine how far the protective efficacy of IPTi depends on spatio-temporal variations of the prevailing incidence of malaria.MethodsOne thousand seventy infants were enrolled in a registered controlled trial on the efficacy of IPTi with sulphadoxine-pyrimethamine (SP) in the Ashanti Region, Ghana, West Africa (ClinicalTrial.gov: NCT00206739). Stratification for the village of residence and the month of birth of study participants demonstrated that the malaria incidence was dependent on spatial (range of incidence rates in different villages 0.6–2.0 episodes/year) and temporal (range of incidence rates in children of different birth months 0.8–1.2 episodes/year) factors. The range of spatio-temporal variation allowed ecological analyses of the correlation between malaria incidence rates, anti-Plasmodium falciparum lysate IgG antibody levels and protective efficacies provided by IPTi.ResultsProtective efficacy of the first SP administration was positively correlated with malaria incidences in children living in a distinct village or born in a distinct month (R2 0.48, p < 0.04 and R2 0.63, p < 0.003, respectively). Corresponding trends were seen after the second and third study drug administration. Accordingly, IgG levels against parasite lysate increased with malaria incidence. This correlation was stronger in children who received IPTi, indicating an effect modification of the intervention.ConclusionThe spatial and temporal variations of malaria incidences in a geographically and meteorologically homogeneous study area exemplify the need for close monitoring of local incidence rates in all types of intervention studies. The increase of the protective efficacy of IPTi with malaria incidences may be relevant for IPTi implementation strategies and, possibly, for other malaria control measures.
Highlights
Intermittent preventive antimalarial treatment in infants (IPTi) is currently evaluated as a malaria control strategy
In most parts of sub-Saharan Africa, individual control measures concentrate on the reduction of parasite transmission through insecticidetreated bed nets and treatment of acute malaria episodes [3], the latter often being inappropriate due to increasing parasite drug resistance [4,5]
An appealing explanation for the observation that the protective efficacy of IPTi increased with the malaria incidence could be the additional influence of acquired immunity, which is dependent on the incidence of malaria
Summary
Intermittent preventive antimalarial treatment in infants (IPTi) is currently evaluated as a malaria control strategy. Among the factors influencing the extent of protection that is provided by IPTi are the transmission intensity, seasonality, drug resistance patterns, and the schedule of IPTi administrations. In most parts of sub-Saharan Africa, individual control measures concentrate on the reduction of parasite transmission through insecticidetreated bed nets and treatment of acute malaria episodes [3], the latter often being inappropriate due to increasing parasite drug resistance [4,5]. It has been assumed that an optimal drug application schedule depends on the half-life of the antimalarial drugs used, the extent of current parasite drug-resistance, the transmission intensity, and the incidence of malaria episodes [10]
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