Plasmodium falciparum gametocyte burden in a Tanzanian low transmission setting

Background Malaria transmission depends on the presence of gametocytes in the peripheral blood of infected human hosts. Understanding malaria infectious reservoirs enables transmission-blocking interventions to target the most important hosts for the disease. This study characterized the distribution of gametocyte carriage as a baseline for clinical evaluation of a Pfs25-based transmission-blocking vaccine candidate in Bagamoyo, Tanzania. Methods A malaria survey was conducted in five villages, between 2022 and 2023. A total of 467 asymptomatic participants; 192 children (5–12 years), 65 adolescents (13–17 years) and 210 adults (18–45 years), were enrolled. Malaria was detected using three methods; Rapid Diagnostic Tests, Light Microscopy, and Quantitative Polymerase Chain Reaction. Geometric mean of the gametocyte density, and weighted arithmetic mean of gametocytes sex ratio were estimated. Results Overall, 23.5% (110/467) of the participants tested positive for malaria parasites, with majority positives (> 92%) being Plasmodium falciparum. The overall gametocytaemia was 5.6%, with percentage positivity of 6.8% (13/192), 6.2% (4/65) 4.3% and (9/210), in children, adolescents and adults, respectively. The geometric mean gametocyte density (gametocytes/µL) was higher in adults (124.6) than in children (71.7) and adolescents (50.5). Regression analysis showed that gametocytes were more likely to be present among male participants than female participants [ORa: 2.79 (95% CI: 1.19–6.59) p = 0.019]. The gametocyte sex ratio in children and adult gametocyte carriers was similar but higher than in adolescents. Conclusion The observed gametocyte densities and distribution across age groups suggest the need for malaria transmission-blocking interventions to target all population, particularly in low transmission settings. The implication of targeting only children may leave residual malaria transmission and re-infection from the left-out groups.