Coalson Jenna E, Walldorf Jenny A, Cohee Lauren M, Ismail Miriam D, Mathanga Don, Cordy Regina Joice, Marti Matthias, Taylor Terrie E, Seydel Karl B, Laufer Miriam K, Wilson Mark L
Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, USA.
Division of Malaria Research, Institute for Global Health, University of Maryland, Baltimore, MD, USA.
Malar J. 2016 Nov 4;15(1):527. doi: 10.1186/s12936-016-1587-9.
In endemic areas, many people experience asymptomatic Plasmodium infections, particularly older children and adults, but their transmission contribution is unknown. Though not the exclusive determinant of infectiousness, transmission from humans to mosquitoes requires blood meals containing gametocytes. Gametocytes often occur at submicroscopic densities, challenging measurement in human populations. More sensitive molecular techniques allow better characterization of gametocyte epidemiologic patterns.
Approximately 30 households were selected from each of eight sites in southern Malawi during two cross-sectional surveys. Blood was sampled from 623 people during the dry season and 896 the following rainy season. Among people PCR-positive for Plasmodium falciparum, mature gametocytes were detected by qRT-PCR. Regression models evaluated predictors of gametocyte carriage and density in the total population and among those with PCR-positive infections.
The prevalence of gametocyte carriage by molecular testing was 3.5% during the dry season and 8.6% during the rainy season, and by microscopy 0.8 and 3.3%, respectively. Nearly half of PCR-positive infections carried gametocytes, regardless of recent symptom status. Among P. falciparum-infected people, only living in unfinished houses and age were significantly associated with gametocyte presence. Infected people in unfinished houses had higher odds of carrying gametocytes (OR 2.24, 95% CI 1.16-4.31), and 31% (95% CI 3-65%) higher gametocyte density than those in finished houses. School-age children (5-15 years), had higher odds than adults (≥16 years) of having gametocytes when infected (OR 2.77, 95% CI 1.47-5.19), but 31% (95% CI 11-47%) lower gametocyte density. Children <5 years did not have significantly higher odds of gametocyte carriage or density when infected than adults.
School-age children frequently carry gametocytes in communities of southern Malawi and represent an under-recognized reservoir of infection. Malaria elimination strategies should address these frequently asymptomatic reservoirs, especially in highly endemic areas. Improved household construction may also reduce the infectious reservoir.
在疟疾流行地区，许多人会感染无症状疟原虫，尤其是大龄儿童和成年人，但其对传播的贡献尚不清楚。虽然不是传染性的唯一决定因素，但从人类传播到蚊子需要含有配子体的血餐。配子体通常以亚微观密度出现，这对人群中的测量构成挑战。更灵敏的分子技术能更好地描述配子体的流行病学模式。
在两次横断面调查中，从马拉维南部八个地点各选取约30户家庭。旱季对623人进行采血，次年雨季对896人进行采血。在恶性疟原虫PCR检测呈阳性的人群中，通过qRT-PCR检测成熟配子体。回归模型评估了总体人群以及PCR检测呈阳性感染者中配子体携带情况和密度的预测因素。
分子检测显示，旱季配子体携带率为3.5%，雨季为8.6%；显微镜检测的携带率旱季为0.8%，雨季为3.3%。无论近期症状状况如何，近一半的PCR检测呈阳性感染者携带配子体。在感染恶性疟原虫的人群中，只有居住在未完工房屋中和年龄与配子体的存在显著相关。居住在未完工房屋中的感染者携带配子体的几率更高（比值比2.24，95%置信区间1.16 - 4.31），且配子体密度比居住在完工房屋中的感染者高31%（95%置信区间3 - 65%）。学龄儿童（5 - 岁）感染时携带配子体的几率高于成年人（≥16岁）（比值比2.77，95%置信区间1.47 - 5.19），但配子体密度低31%（95%置信区间11 - 47%）。5岁以下儿童感染时，配子体携带率或密度并不比成年人显著更高。
在马拉维南部社区，学龄儿童经常携带配子体，是一个未得到充分认识的感染源。疟疾消除策略应针对这些经常无症状的感染源，尤其是在高度流行地区。改善房屋建设也可能减少感染源。
