High Prevalence of Asymptomatic Malaria in Bandafassi, South-east of Senegal: Challenge for Malaria Elimination

Background: Malaria control and elimination strategies are based on levels of transmission that are usually determined by data collected from health facilities. In endemic areas, asymptomatic malaria is thought to represent the majority of infections and is therefore not diagnosed nor treated. As a consequence, they are missed when analyzing data due to the lack of visiting the health facilities unless they are sick. Therefore, there might be an underestimation of the malaria prevalence resulting in inadequate control strategies. In addition, these untreated asymptomatic cases maintain transmission making it difficult or impossible to reach malaria elimination goals. Thus, the aim of this study was to determine the prevalence of asymptomatic malaria in southeastern Senegal. Methods: A cross sectional study was conducted among asymptomatic individuals (N = 122) living in the village of Andiel located in Bandafassi, Kedougou which consisting of about 200 inhabitants during the malaria transmission season in late October 2019. For each individual without malaria symptoms and who consented to participate in the study, a rapid diagnosis test (RDT) was performed in the field. Results were confirmed in the laboratory with nested PCR and photo-induced electron transfer (PET-PCR). Results: Malaria prevalence was 70.25% with PET-PCR, 41.80% with RDT and 41.32% based on the nested PCR. The majority of the study population; 92.94% was infected with a single species (mono-infection) and 7.06% had two or three species of Plasmodium. P. falciparum was predominant and represented 90.22% of the infections, while 6.52% were due to P. ovale and 3.26% to P. malariae. RDT detected more malaria cases than nested PCR among children and in individuals aged fifteen years and older; PET-PCR detected more cases (64.70%) than nested PCR (62%) and RDT (52.94%) in this age group.Conclusion: Asymptomatic infection is a threat to malaria elimination. In southeastern Senegal, where the transmission is the highest in the country, malaria control strategies should address asymptomatic cases at the community level. This high prevalence of asymptomatic malaria observed suggests that this area is eligible for mass drug administration. Moreover, non-falciparum species could be more common and its prevalence should be determined countrywide.