Gametocyte Carriages of Plasmodium falciparum (pfs25) and Plasmodium vivax (pvs25) during Mass Screening and Treatment in West Timor, Indonesia a Longitudinal Prospective Study

Abstract Background: Three rounds of mass screening and treatment (MST) demonstrated no effect on Plasmodium falciparum and P. vivax incidence in West Timor, Indonesia. This study nested within that trial evaluated the effect of MST on gametocyte carriage.Methods: Microscopy and PCR diagnostics were applied to study subjects through 3 months of MST involving dihydroartemisinin-piperaquine (DHP) and primaquine based on infecting Plasmodium species. RT-qPCR targeting the pfs25 and pvs25 sequences was conducted to detect and quantify gametocytes in blood samples of P. falciparum and P. vivax- infected subjects. Data from the baseline and endpoint were compared (p<=0.05 as the significance threshold).Results:Between baseline and endpoint, prevalence remained unchanged for P. falciparum (6%=52/811 versus 7%=50/740, p=0.838) and decreased slightly for P. vivax (24%=192/811 versus 19%=142/740, p=0.035). No significant difference was observed in gametocyte carriage rates for either P. falciparum (43%=19/44 versus 59%=23/39, OR & 95%CI=1.89, 0.72-4.97) or P. vivax (39%=49/125 versus 37%=39/106, OR & 95%CI=0.90, 0.51-1.59). Despite the insignificant differences between the two time points, the majority of positive subjects at the endpoint were newly parasitemic individuals (new infections) (Pf:92%=46/50, Pv: 65%=93/142). This result was similarly demonstrated for the transmissible stage - where new gametocyte carriers dominated endpoint positive subjects (Pf: 96%=22/23, Pv: 95%=37/39). Conclusion:Although three rounds of MST decreased individual parasitemia and gametocytemia based on diagnosis and treatment, this failed to impact malaria prevalence at a population level due to the development of new infected individuals that can sustain transmission. These observations in part explains why MST failed to impact transmission of malaria in this transmission context.