Plasmodium falciparum carriage in a population under long-term, intensive malaria control in Kedougou region, Senegal: a 1-year cohort study.

BACKGROUND

In Sahelian Africa, successful interventions against malaria include vector control, improved access to care, and seasonal malaria chemoprevention (SMC) in children. However, malaria incidence has increased in the past 5 years. Up-to-date evidence is necessary to design additional interventions and restore progress towards elimination. In this study, we aimed to describe subclinical Plasmodium falciparum infections in the general population and understand the changes in prevalence, parasite densities, and clinical incidence across age groups and seasons, and to identify factors associated with P falciparum carriage in Kedougou, Senegal's most affected region.

METHODS

We included all individuals older than 6 months from randomly selected households of four villages in a 1-year open cohort. During four surveys spanning the dry and wet seasons, we collected sociodemographic and behavioural data, and detected P falciparum using quantitative PCR on capillary dried blood samples. We analysed risk factors associated with P falciparum carriage using multilevel logistic regression.

FINDINGS: We included 763 participants from 69 households, and they were followed up from April 13, 2021, to March 30, 2022. P falciparum prevalence was lowest in SMC-eligible children (aged <10 years) and remained below 10% across wet and dry seasons. Older age groups had similar dry season prevalence at baseline (10-15%). During the wet season, prevalence increased in individuals aged 15-24 years (32·1%) and 35-49 years (24·7%). The highest clinical burden was in participants aged 10-14 years (527 cases per 1000 person-years) and 15-19 years (631 cases per 1000 person-years), over five-fold higher than children aged 6 months to 4 years (93 cases per 1000 person-years). Outdoor night-time activity was associated with P falciparum infection.

INTERPRETATION: In this setting, ongoing intensive control reduced malaria in SMC-eligible children. Older individuals bear an important clinical burden and harbour high prevalence during the wet season. Elimination-oriented interventions must tackle the parasite reservoir, involving whole communities and specifically young adults.

FUNDING: Excellence Initiative of Aix-Marseille University-A*MIDEX, a French Investissements d'Avenir programme: the MARS project (A*Midex International 2018).

TRANSLATION: For the French translation of the abstract see Supplementary Materials section.