IntroductionIn areas of seasonal malaria, resuming transmission every wet season relies on persistent asexual parasites during dry season that maintain the ability to produce gametocytes until the mosquito population resurges following the start of annual rains. Although human asymptomaticP. falciparumreservoirs in the dry season are widely recognized, the longitudinal dynamics of parasite sexual commitment and gametocytogenesis remain unclear.MethodsWe compared the expression of genes related with sexual commitment and gametocytogenesis ofP. falciparum, the density and proportion ofP. falciparumgametocytes, and the blood concentrations of phospholipids potentially involved in gametocytogenesis from asymptomatic subjects at the end of the dry season versus subjects with symptomatic malaria in the wet season. Furthermore, we verified whether number and proportion of gametocytes in asymptomatic vs clinical cases had similar trends in areas of seasonal and perennial transmission settings. Finally, we adapted a within-host mathematical model considering asexual parasites, sexually committed parasites, and gametocytes to infer the dynamics of gametocyte number and proportion asP. falciparuminfections progress.ResultsWe found that transcripts of genes specific of late-stage gametocytes were predominantly upregulated in asymptomatic infections at the end of the dry season, which also showed increased proportions of circulating mature gametocytes compared to clinical malaria cases. On the other hand, blood densities of gametocytes and asexual parasites were lower in chronic asymptomatic individuals compared to clinical malaria. In addition, the levels of parasite transcripts involved in sexual commitment were unaltered throughout the year.DiscussionOur experimental data in combination with mathematical modelling support a scenario in which gametocyte density and proportion diverge as infections progress from recent transmission to chronic carriage, without significant alterations in the rate of sexual commitment over time.
