P. falciparum gametocyte density and infectivity in peripheral blood and skin tissue of naturally infected parasite carriers in Burkina Faso.

BACKGROUND: Plasmodium falciparum transmission depends on mature gametocytes that can be ingested by mosquitoes taking a bloodmeal on human skin. Although gametocyte skin sequestration has long been hypothesized as important contributor to efficient malaria transmission, this has never been formally tested.

METHODS: In naturally infected gametocyte carriers from Burkina Faso, we assessed infectivity to mosquitoes by direct skin feeding and membrane feeding. We directly quantified male and female gametocytes and asexual parasites in: i) finger prick blood, ii) venous blood, iii) skin biopsies, and in pools of mosquitoes that fed iv) on venous blood or, v) directly on skin. Gametocytes were visualized in skin tissue by confocal microscopy.

RESULTS: Whilst more mosquitoes became infected when feeding directly on the skin compared to venous blood (odds ratio 2.01; 95% CI 1.21 - 3.33, p = 0.007), concentrations of gametocytes in the subdermal skin vasculature were not higher compared to other blood compartments; only sparse gametocytes were observed in skin tissue.

DISCUSSION: Our data strongly suggest that there is no significant skin sequestration of P. falciparum gametocytes. Gametocyte densities in peripheral blood are thus informative for predicting onward transmission potential to mosquitoes and can be used to target and monitor malaria elimination initiatives.