The dynamics of asymptomatic Plasmodium spp. infections following 10 years of malaria control interventions in Northern Sahelian Ghana

Current interventions targeting malaria control in sub-Saharan Africa (SSA) are focused on Plasmodium falciparum, the most prevalent species infecting humans. Despite renewed efforts for malaria elimination in SSA, little attention has been paid to the neglected parasites P. malariae, P. ovale spp., and P. vivax and the impact of interventions like long-lasting insecticidal nets (LLINs), indoor residual spraying (IRS) with non-pyrethroid insecticides, and/or seasonal malaria chemoprevention (SMC) on these minor Plasmodium spp. To address this research gap, the aim of this observational study was to assess the impact of two sequential interventions, IRS and SMC combined with LLINs, on the Plasmodium spp. reservoir, with particular emphasis on the non-falciparum minor species, in Bongo District, an area characterized by high seasonal transmission in the Northern Sahelian belt of Ghana. Using an interrupted time-series study design, five age-stratified surveys, each of ~2,000 participants, were undertaken at the end of the wet seasons between 2012 and 2022. Across this 10-year study period, infections with P. malariae and P. ovale spp. were detected using a species-specific PCR targeting the 18S rRNA gene, while P. vivax was not detected. In 2015, following IRS, the prevalence of the minor Plasmodium spp. declined in all ages from baseline in 2012, with participants being significantly less likely to be infected with P. malariae (13.7% vs 1.4%) and P. ovale spp. (5.7% vs 0.4%). Despite this decline, in 2017, 32 months after IRS was discontinued and SMC was introduced, the prevalence of P. malariae (2.9%) and P. ovale spp. (4.0%) rebounded, with approximately a 2- and 10-fold increase, respectively. This rebound in the minor species was observed in all age groups, except for the younger children (< 5 years) targeted by SMC. Finally, when we examined this population in 2020 and 2022 after continued deployment of SMC, the prevalence of P. malariae continued to increase (7.4% and 5.8%), while the prevalence of P. ovale spp. declined (2.6% and 1.3%). Results show that both IRS and SMC were effective not only against P. falciparum but also reduced the prevalence of P. malariae and P. ovale spp. in Bongo District. Going forward, molecular diagnostics will be critical to identify changes in the submicroscopic reservoir of the minor Plasmodium spp. found in adolescents and adults and to achieve malaria elimination in this region of Ghana.