Dynamics of asymptomatic malaria infection and associated factors in South Benin

Abstract Introduction Asymptomatic malaria infection is now recognized as a potential threat to malaria control. However, its prevalence and its dynamics are poorly documented especially in a perennial context of high seasonal transmission. A longitudinal study was conducted in southern Benin to investigate the dynamics of asymptomatic malaria infection and to identify factors influencing it. Methods A cohort of 377 participants was recruited, stratified into three age groups (under 5 years, between 5 and 15 years, over 15 years). After inclusion, two visits were made one-month apart between August and November 2021. Malaria infection was diagnosed by microscopy and PCR and questionnaires were administered to the participants. The dynamics of malaria infection, both submicroscopic (positive PCR / negative blood smear) and microscopic (positive blood smear), and related factors were determined using a mixed ordinal polytomous regression model and a multistate Markov model. Results The human infectious reservoir consisted primarily of asymptomatic submicroscopic infections (289/512 (56.4%)), followed by asymptomatic microscopic infections (182/512 (35.5%)) and symptomatic infections (41/512 (8%)). The prevalence of asymptomatic infection was highly related to age-group (5-15 years: OR: 4 .12 [2.55-6.67] and > 15 years: OR: 2.80 [1.73-4.54] compared to the under 5 years old group). The children under 15 years with asymptomatic infection had the highest risk of becoming symptomatic. The mean duration of asymptomatic infections in 5-15-year-olds was the longest (76.7 days (53.8-109.1)). Conclusions This study revealed a persistent asymptomatic malaria reservoir over the follow-up period, with substantial variations between age-groups. These findings are important elements to consider for an optimal deployment of malaria control interventions. Key messages • Infection dynamics vary considerably by age group, underlining the need for age-targeted malaria control strategies to improve the effectiveness of interventions. • Submicroscopic malaria infections constitute the majority of the human infectious reservoir in southern Benin, with the highest prevalence observed in children aged 5-15 years.