Increased gametocyte production and mosquito infectivity in chronic versus incident Plasmodium falciparum infections

We longitudinally assessed P. falciparum parasite kinetics, gametocyte production and infectivity in incident infections that were naturally acquired following infection clearance and in chronic asymptomatic infections in Burkina Faso. 92% (44/48) of the incident cohort developed symptoms and were treated within 35 days, compared to 23% (14/60) of the chronic cohort. All but two individuals with chronic infection were gametocytaemic at enrollment, whereas only 35% (17/48) in the incident cohort developed gametocytes within 35 days. The relative abundance of ap2-g transcripts was positively associated with conversion to gametocyte production (i.e. the ratio of gametocytes at day 14 to ring stage parasites at baseline) and was higher in chronic infections. Parasite multiplication rate, assessed by daily molecular parasite quantification, was positively associated with prospective gametocyte production. Most incident infections were cleared before gametocyte density was sufficiently high to infect mosquitoes. In contrast, chronic, asymptomatic infections represented a significant source of mosquito infections. If present, gametocytes were significantly less infectious if concurrent with malaria symptoms. Our observations support the notion that malaria transmission reduction may be expediated by enhanced case management, involving both symptom-screening and infection detection.