Madagascar P. vivax Invasion of Duffy-negative Red Cells

描述(申请人提供)：今天，至少有26亿人生活在间日疟原虫传播的危险地区；每年有1.06亿-3.13亿间日疟病例。虽然Duffy血型阴性(Duffy(-))被认为赋予了对间日疟的抵抗力，但我们最近的发现表明，间日疟原虫已经获得了感染红细胞并在马达加斯加Duffy(-)人群中导致疾病的能力。我们对学龄儿童的调查显示，间日疟原虫在8.8%的无症状Duffy(-)儿童中呈阳性。我们还观察到，在体内药物疗效调查期间报告接受治疗的达菲(-)人群中，有4.9%的人患有单感染间日疟原虫临床疾病；血液涂片诊断证实了间日疟原虫。有趣的是，使用6个非连锁微卫星标记进行的初步群体研究表明，Duffy(-)感染是由多个间日疟原虫株引起的。虽然我们的结果表明间日疟原虫在马达加斯加的入侵可以独立于红细胞的Duffy血型抗原发生，但我们不知道入侵是依赖还是独立于寄生虫的所谓的Duffy结合蛋白(PvDBP)，这种寄生虫配体被认为对入侵人类红细胞是必不可少的。通过对PvDBP基因座的DNA测序，我们发现了一个在Duffy(-)感染中过度表达的等位基因。此外，最近的全基因组测序显示，马达加斯加间日疟原虫株(和马达加斯加以外没有间日疟原虫株)携带PvDBP重复。总体而言，我们的发现表明，马达加斯加的间日疟原虫正在进化出新的红细胞感染机制。为了开始了解间日疟原虫是如何获得感染Duffy(-)红细胞的能力的，我们建议在对马达加斯加间日疟原虫菌株进行深入的细胞和分子生物学分析的同时，研究寄生虫种群的群体遗传特征。这些研究得出的数据将使我们能够实现以下具体目标。目的1-确定间日疟原虫株系与Duffy(-)人群对间日疟原虫血液期感染和临床疟疾易感性的关系。目的2-评估间日疟原虫红细胞结合配体与人红细胞的相互作用对裂殖子附着和人红细胞侵袭的影响。目的3-检测间日疟原虫马达加斯加株对Duffy(-)和Duffy(+)红细胞的体外侵袭途径。我们的研究将确定达菲(+)和达菲(-)人群对间日疟原虫病的不同易感性。Planne的体外研究将提供有关间日疟原虫红细胞入侵新机制的洞察力，特别强调Duffy非依赖性入侵。最后，我们将确定间日疟原虫与Duffy(+)和Duffy(-)红细胞结合和入侵所涉及的分子变异是否表明马达加斯加间日疟原虫株有传播到其他种群的能力。

DESCRIPTION (provided by applicant): Today at least 2.6 billion people live in areas of risk for Plasmodium vivax transmission; 106 - 313 million cases of vivax malaria annually. While Duffy blood group negativity (Duffy (-)) has been considered to confer resistance to vivax malaria, our recent findings show that P. vivax has gained the capacity to infect erythrocytes and cause disease in Duffy (-) people in Madagascar. Our surveys of school-aged children revealed P. vivax PCR-positivity in 8.8% of asymptomatic Duffy (-) children. We also observed mono-infection P. vivax clinical disease in 4.9% of Duffy (-) people who reported for treatment during in vivo drug efficacy surveys; blood smear diagnosis confirmed P. vivax. Interestingly, preliminary population studies using 6 unlinked microsatellite markers suggested that Duffy (-) infections were caused by multiple P. vivax strains. While our results indicate that P. vivax invasion in Madagascar can occur independent of the erythrocyte's Duffy blood group antigen, we do not know if invasion is dependent or independent of the parasite's 'so-called' Duffy binding protein (PvDBP), the parasite ligand considered essential for invasion of human red blood cells. By DNA sequencing the PvDBP locus we have identified one allele to be over-represented in Duffy (-) infections. Additionally, recent whole genome sequencing has revealed that Malagasy P. vivax strains (and no P. vivax strains outside Madagascar) carry a PvDBP duplication. Overall, our findings suggest that P. vivax in Madagascar is evolving new erythrocyte infection mechanisms. To begin understanding how P. vivax has gained capacity to infect Duffy(-) erythrocytes we propose to study population genetic features of the parasite population while performing in-depth cell and molecular biological analysis of P. vivax strains of Madagascar. Resulting data from these studies will allow us to address the following Specific Aims. Aim 1 - Determine associations between P. vivax strains and susceptibility of Duffy (-) people to P. vivax blood-stage infection and clinical malaria. Aim 2 - Assess interactions between P. vivax erythrocyte binding ligands and human erythrocytes that influence merozoite attachment and human red cell invasion. Aim 3 - Test alternative invasion pathways of Malagasy P. vivax strains in vitro for Duffy (-) and Duffy (+) erythrocytes. Our studies will determine differential susceptibility of Duffy (+) and Duffy (-) people to P. vivax disease. Planne in vitro studies will provide insight regarding new P. vivax erythrocyte invasion mechanisms, with special emphasis on Duffy-independent invasion. Finally, we will determine whether molecular variations involved in P. vivax binding to, and invasion of Duffy (+) and Duffy (-) erythrocytes indicates capacity of Madagascar P. vivax strains to spread into other populations.