Determinants of malaria transmission by submicroscopic gametocytemia

摘要 尽管疟疾控制工作在过去十年中大大减少了疟疾负担， 无症状感染者的数量仍然存在，阻碍了消灭疟疾。大多数无症状 携带者携带的寄生虫可以通过PCR检测到，但被目前的快速诊断测试所遗漏， 显微镜这些亚显微感染是大规模药物管理努力的一个理由。然而 亚显微感染在持续传播中的作用尚不清楚。事实上，疟疾寄生虫 负责人对蚊子的感染，配子体，可能不会达到大多数传播水平 亚显微感染的证据我们建议，更好地了解配子介导的传播， 低密度可以导致设计更好的策略来阻断寄生虫传播。目标1 该提案将使用蚊子喂养试验来确定无症状水库中的谁具有传染性， 蚊子，研究配子体密度，性别比例和菌株多样性在确定 可传递性。我们将使用直接皮肤喂养来测量人与蚊子的传播， 比更常用的膜饲养测定法更灵敏的人类感染性测量。目的2 将决定亚显微感染持续存在并发展感染性配子细胞的倾向 时间在这两个目标中，下一代测序技术将用于区分个体 配子体菌株，以更好地了解混合配子体群体的组成， 个体随时间变化并影响传播，以及密集的控制工作是否选择了 能够在低密度下持续存在而不引起症状的寄生虫菌株。这些信息对于 了解是什么因素维持了亚显微配子体载体的传播， 传输失败。最后，Aim 3部署了一种与现场相关的新型诊断测试， 重塑消灭疟疾战略。我们假设Gam-RDT的敏感性，一个横向流 免疫测定法检测唾液中一种新发现的配子体标记物， 传播发生的密度，使其成为一个有价值的现场工具，用于识别寄生虫携带者， 传染源我们将在坦桑尼亚的巴加莫约进行研究， 病例在过去十年中有所减少，高达45%的学龄儿童继续无症状 通过高灵敏度PCR检测寄生虫血症。我们经验丰富的临床试验专家团队， 昆虫学家和疟疾流行病学和遗传多样性方面的国际专家将建立 疟疾如何从亚显微配子体载体传播的证据基础， 密集的控制努力已经成功地减少了全球疟疾负担，但可能还不够 来消灭这种古老的人类寄生虫

ABSTRACT Even as malaria control efforts have achieved great reductions in malaria burden over the last decade, vast numbers of asymptomatic infection exist and present an obstacle to malaria elimination. Most asymptomatic carriers harbor parasites that are detectable by PCR but missed by current rapid diagnostic tests and microscopy. These submicroscopic infections are one rationale for mass drug administration efforts. Yet the role of submicroscopic infections in sustaining transmission is unknown. In fact, the malaria parasites responsible for human to mosquito infection, gametocytes, may not achieve transmissible levels in the majority of submicroscopic infections. We propose that a better understanding of gametocyte-mediated transmission at low densities can lead to the design of better strategies to interrupt parasite transmission. Aim 1 of this proposal will use mosquito feeding assays to define who within the asymptomatic reservoir is infectious to mosquitoes, investigating the role of gametocyte density, sex ratio, and strain diversity in determining transmissibility. We will use direct skin feeding to measure human to mosquito transmission, considered a truer, more sensitive measure of human infectiousness than more commonly used membrane feeding assays. Aim 2 will determine the propensity for submicroscopic infections to persist and develop infective gametocytes over time. In these two aims, next generation sequencing techniques will be used to distinguish individual gametocyte strains to better understand how the composition of mixed gametocyte populations within individuals changes over time and affects transmission, and whether intensive control efforts are selecting for parasite strains that are able to persist at low densities without causing symptoms. This information is crucial to understanding what factors sustain transmission from submicroscopic gametocyte carriers even as overall transmission wans. Finally, Aim 3 deploys a field-relevant novel diagnostic test that has the potential to reshape malaria elimination strategies. We hypothesize that the sensitivity of Gam-RDT, a lateral flow immunoassay that detects a newly discovered gametocyte marker in saliva, approximates the gametocyte density at which transmission occurs, making it a valuable field tool for identifying parasite carriers who make up the infectious reservoir. We will conduct our study in Bagamoyo, Tanzania, an area where, although malaria cases have decreased over the last decade, up to ~45% of schoolchildren continue to have asymptomatic parasitemia detectable by highly sensitive PCR. Our team of experienced clinical trialists, leading malaria entomologists, and international experts in malaria epidemiology and genetic diversity will establish the evidence base for how malaria transmission from submicroscopic gametocyte carriers occurs in the face of intensive control efforts that have successfully reduced the global malaria burden, but will likely not be enough to eradicate this age-old human parasite.