Naturally Acquired Immune Responses to Antigens of the Sexual and Asexual Stages of Plasmodium Falciparum in the Southern and Central Regions of Senegal

In Senegal, despite numerous malaria control interventions, transmission is still seasonal. Malaria transmission depends on the presence of infectious parasites in the sexual stage in human peripheral blood. Immune responses acquired naturally at these or other stages can affect malaria transmission, resulting in protection against malaria, reduced transmission, and also form the basis for the development of transmission-blocking vaccines. To evaluate the antibody response profile against the asexual antigens PfAMA1, PfMSP119, Pf GLURP R2 and the sexual antigens Pfs230C1, Pfs48.45.6C in inhabitants naturally exposed to malaria in areas with different levels of transmission in Senegal. A cross-sectional study was carried out at the end of the transmission season in central (Keur Socé) and southern (Saraya) Senegal in 2018. We included 1106 asymptomatic volunteers aged 5 and over. Capillary blood was collected from each participant for an RDT, 2 slides for microscopy and a dried blood spot samples for immunology. A Luminex serological multiplex bead assay was then used to assess Plasmodium falciparum seroprevalence Our study population was characterized by a very young population with a median age of 12  15 years. The parasite prevalence of Plasmodium falciparum was 21.75% and 2.75% by RDT and 22.1% and 2.2% by microscopy for the southern and central regions respectively. Two other plasmodial species were found in Saraya, with prevalences of 1.61% for P. malariae and 0.18% for P. ovale. The mean seroprevalences of antibodies against three asexual blood-stage antigens (PfAMA1, PfGLURP and PfMSP119) and two sexualstage antigens (Pfs48.45.6C and Pfs230C1) were significantly higher in Saraya. In Keur Socé, the mean seroprevalence of antibodies against the PfAMA1 antigen was highest (1.83%), while in Saraya, PfMSP119 was highest (49.91%). The antigenicity of these proteins depended on endemicity levels, as antibody prevalence was statistically different in the two sites and increased with transmission intensity. With the exception of anti-Pfs48.45.6C antibody levels, all other antibody responses increased with age. Overall, these data indicate that the seroprevalence and antivody levels of individuals with antibodies recognizing all five antigens increase with exposure to infection, and that these antibodies may contribute to immunity against parasites. Children receiving SMC should also be monitored, as we have noted a loss of immunity in this group.