Tools and strategies for malaria control such as artemisinin-based combination therapy, long-lasting insecticide-treated bed nets, intermittent preventive treatment in pregnancy, and intermittent preventive treatment in infancy and seasonal malaria chemoprevention in children have shown efficacy in malaria control (1, 10). In Bandiagara, following implementation of long-lasting insecticide-treated bed nets, rapid diagnostic tests, and artemisinin-based combination therapy, a study showed a comparable incidence to what was observed in 1999, prior to implementation of these control strategies (7). Seasonal malaria chemoprevention was scaled up in 2016 in Mali, and in 2017–2018, the health district of Bandiagara benefited from a large distribution of long-lasting insecticide-treated bed nets and indoor residual spraying. As new interventions need to be monitored for proper implementation and potential impact, we measured the incidence of malaria in the pediatric population, predicting a decline.
A cohort of three hundred children was followed using active and passive surveillance to capture all clinical episodes of malaria that occurred in the cohort during the study period. This study showed a reduction of malaria incidence among under 5-year-olds.
The low prevalence of infection (Fig. 2) attests the reduction of the transmission intensity and may be due to the combination of implementation of SMC, use of LLITN and IRS in Bandiagara. The highest prevalence of infection was observed in the dry season May 2018 (Fig. 2). All parasite carriers at that period were asymptomatic. The highest prevalence of malaria infection was noticed in children aged above 10 years old.
The prevalence of anaemia rose in October 2018, peaking at 18.2% the following month in the 0–5 years age group. The prevalence remained less than 5% in older age groups irrespective of month. This rise paralleled a rise in malaria prevalence, but other contributors to anaemia include malnutrition. At our study site, a food shortage is generally observed from August to December, which could contribute to the high prevalence of anaemia in that period in young children, who are also more susceptible to other infections than older children.
The overall malaria incidence rate was 0.5 episodes/person-year; the age-specific incidence was 0.29, 0.57, and 0.6 episodes per person-year observed, in the 6 months-5 years, 6–10 years, and above 10 years old groups, respectively (Table 2). Children aged 6 months to 5 years had a lower malaria incidence than those older than 5 years of age. This is unusual, given that in high transmission settings, the highest malaria incidence has classically been seen in younger children (11).
Previous studies in Bandiagara determined an incidence of malaria of 1.7 episodes per person / 24 weeks in 1999, and 1.4 episodes per person-years from 2009–2013. The decrease in malaria incidence established by this current study may due to the combined effect of the use of long-lasting insecticide-treated bed nets, seasonal malaria chemoprevention, and IRS, suggesting that malaria may be eliminated with the proper implementation of all of the prevention tools available today. Older children (more than five years old) experienced more malaria clinical episodes than the youngest group. These findings confirm the age shift in the susceptibility to malaria recently reported by multiple authors in regions where control strategies were implemented (7, 12, 13).
One additional consideration for malaria elimination is that a previous study revealed the presence of P. vivax in Duffy blood group negative children residing in our study site (8). We did not perform molecular testing for P. vivax in this study. The decline in the incidence of Plasmodium falciparum infection has generated enthusiasm for the elimination of malaria. However, there is growing evidence of P. vivax infection in Duffy blood group negative populations (14–17), and the species shift (18). may jeopardize malaria control efforts. Particular attention needs to be given to this species through extensive prevalence studies and control program adaptations.
Some limitations of this study include the lack of entomological parameters of transmission to support clinical findings and the relative short study period.