Plasmodium 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 blood meal 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
finger-prick and venous blood samples, skin biopsy samples, and in of
mosquitoes that fed on venous blood or directly on skin. Gametocytes were
visualized in skin tissue with confocal microscopy. Results Although more
mosquitoes became infected when feeding directly on skin then when feeding
on venous blood (odds ratio, 2.01; 95% confidence interval, 1.21–3.33; P =
.007), concentrations of gametocytes were not higher in the subdermal skin
vasculature than in 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.

背景 恶性疟原虫（Plasmodium falciparum）的传播依赖成熟配子体，当蚊虫在人体皮肤吸血时可摄入此类配子体。长期以来，学界假设配子体皮肤滞留是高效疟疾传播的重要促成因素，但该假说从未经过正式验证。
方法 本研究纳入来自布基纳法索的自然感染恶性疟原虫配子体携带者，通过皮肤直接喂食法与膜喂食法评估其对蚊虫的感染性。我们分别对指尖血、静脉血样本、皮肤活检样本，以及吸食静脉血或直接吸食皮肤血液的蚊虫体内的雄、雌配子体与无性体寄生虫进行定量检测，并通过共聚焦显微镜（confocal microscopy）对皮肤组织中的配子体进行可视化观察。
结果 尽管直接吸食皮肤血液的蚊虫感染率高于吸食静脉血的蚊虫（优势比=2.01；95%置信区间：1.21~3.33；P=0.007），但皮下血管中的配子体浓度并未高于其他血液腔室，且仅在皮肤组织中观察到少量配子体。
讨论 本研究数据强烈表明，恶性疟原虫配子体并未发生显著的皮肤滞留。因此，外周血中的配子体密度可用于预测其向蚊虫传播的潜在能力，亦可用于靶向监测疟疾消除相关行动。