Development of novel therapeutics for Babesia microti infection

描述(申请人提供)：顶复合体红细胞内寄生虫微小巴贝斯虫是一种新出现的人类病原体，也是人类巴贝斯虫病的主要原因，巴贝斯病是一种在美国流行的类似疟疾的疾病。这种病原体通过扁虱媒介肩部硬蜱传播给人类，并通过输血传播给无症状的微小硬蜱感染捐赠者。巴贝斯虫病是一个主要的公共卫生问题，因为患严重疾病的风险人群(50岁以上和免疫系统受损的任何年龄的人)正在增加。目前推荐的治疗方法为阿奇霉素+阿托瓦酮或克林霉素+奎宁。由于已知的抗疟疾活性，这些药物组合首先被评估其抗巴贝斯虫的活性。有了这些药物和其他辅助措施，如换血，在需要住院的感染患者中，死亡率为9%，在免疫低下的宿主中，死亡率接近28%。存活下来的患者可能会经历一年以上的复发性寄生虫病，需要更长的治疗时间。巴贝斯症尽管接受了药物治疗，但仍能存活下来的原因尚不清楚。更好地了解寄生虫的新陈代谢、多样性、毒力和组织分布，对于开发更有效的治疗人类巴贝斯虫病的方法至关重要。为了实现这一目标，我们已经完成了基因组和转录组分析，并开始对七株微小杆菌临床分离株的基因组进行彻底的注释和代谢机制的重建。我们的初步研究结果表明，微小芽孢杆菌在不同菌株之间表现出基因变异。这些差异可能解释了它们在增殖率和宿主选择性(小鼠与仓鼠)方面的显著差异。我们还确定了两条关键的代谢途径，非甲氧戊酸(MEP)途径和叶酸生物合成途径(FBP)，这两条途径可以作为FDA批准的药物的靶点。为了全面表征这些药物在体内对抗微小杆菌感染的疗效，建立了微小杆菌感染的小鼠模型。 必须更清楚地界定可能导致寄生虫血症复发的寄生虫持续存在的部位。因此，这项建议旨在(1)确定从经历过轻度或严重疾病的非免疫低下患者中分离的两种微型杆菌原型菌株在小鼠体内的寄生虫血症动力学和持续部位；以及(2)评估针对微型杆菌的MEP和FBP途径的药物在解决寄生虫血症和消除感染方面的疗效。这些探索性研究的成功完成将有助于确定微小杆菌致病的潜在机制，并为未来的临床研究奠定基础，以评估这些药物在现有治疗方法失败的情况下治疗人类巴贝斯虫病的疗效。

DESCRIPTION (provided by applicant): The apicomplexan intraerythrocytic parasite Babesia microti is an emerging human pathogen and the primary cause of human babesiosis, a malaria-like illness endemic in the United States. The pathogen is transmitted to humans by the tick vector, Ixodes scapularis, and by transfusion of blood from asymptomatic B. microti-infected donors. Babesiosis is a major public health concern because the population at risk for severe disease (people over the age of 50 and of any age with compromised immune systems) is increasing. Presently, drug combinations of azithromycin+atovaquone or clindamycin+quinine are recommended therapies. These drug combinations were first evaluated for their anti-babesia activity because of their known antimalarial activity. With these drugs and other supportive measures such as exchange transfusion, the mortality rate is 9% in infected patients requiring hospitalization and approaches 28% in immunocompromised hosts. Patients who survive may experience recrudescent parasitemia for more than a year, requiring more prolonged therapy. The reasons that Babesia can persist despite drug therapy remain unknown. A better understanding of the parasite metabolism, diversity, virulence and tissue distribution are critical for the development of more effective therapies for treatment of human babesiosis. Towards this goal, we have completed genomic and transcriptomic analyses and initiated thorough annotation of the genomes and reconstruction of the metabolic machineries of seven B. microti clinical isolates. Our preliminary findings indicate that B. microti exhibits genotypic variations among strains. These variations may account for their notable differences in rate of proliferation and host selectivity (mice vs hamsters). We have also identified two key metabolic pathways, the non-mevalonate (MEP) pathway and the folate biosynthesis pathway (FBP), which can be targeted by drugs already approved by the FDA. In order to fully characterize the efficacy of these drugs against B. microti infection in vivo, a mouse model of B. microti infection must be more clearly defined in terms of sites of parasite persistence that may lead to recrudescence of parasitemia. Accordingly, this proposal aims to (1) define in mice the kinetics of parasitemia and sites of persistence of two prototype B. microti strains isolated from non-immunocompromised patients who experienced mild or severe disease; and (2) assess the efficacy of drugs that target the MEP and FBP pathways of B. microti to resolve parasitemia and eliminate infection. Successful completion of these exploratory studies will help define mechanisms underlying B. microti pathogenesis and set the stage for future clinical studies to evaluate the efficacy of these drugs for treatment of human babesiosis in situations when current therapies fail.