Recurrent treatment: Effect on rural and urban S. mansoni population structure

描述（由申请人提供）：当地曼氏血吸虫种群中存在的生物异质性很难研究，但这种多样性和当地寄生虫种群动态是疾病的重要危险因素；它们可能有助于药物设计，并可能影响控制策略。S. mansoni的控制方案以每2-3年重复化疗为中心，以减少感染强度，从而降低发病率。流行受到的影响要小得多，传播也没有中断，因为这些人群迅速恢复。在很大程度上，由于缺乏区分蠕虫亚群的工具和方法，人们不知道周期性种群收缩和再扩张对血吸虫生物学的最终影响。我们已经确定了7个多态微卫星标记，它们的行为类似于单拷贝位点，具有物种特异性，并对从寄生虫卵中分离的DNA产生可解释的模式。此外，为了优化采样，我们开发了从粪便中分离寄生虫卵DNA的方法，以及利用汇集样本的等位基因频率而不是离散基因型的统计方法。为了了解反复化疗如何改变曼氏梭菌种群结构，本方案将通过从感染个体的粪便中分离卵DNA并进行基因分型，直接确定曼氏梭菌的等位基因频率分布。然后，这些等位基因频率将与每年化疗前后寄生虫的区域和微地理分布有关。利用我们开发的工具，该项目将：1)确定微观地理与亚种群分布和基因流动的关系；2)确定广泛的化疗如何改变种群结构；3)确定化疗后持续存在的种群与治疗前种群的关系；4)测量迁移或常住人口增加对血吸虫种群恢复的贡献；5)评估当地寄生虫传播与移民对城市疫源地的贡献。6)治疗前后城市人群与农村人群的对比。人口结构将通过人口固定指数（Fsr）和有效人口规模（Ne）和移民率(m)的估计进行比较。混合库存分析也将用于分析迁移。

DESCRIPTION (provided by applicant): The biologic heterogeneity that exists within local Schistosoma mansoni populations is difficult to study, yet this diversity and local parasite population dynamics are important risk factors for disease; they may assist drug design and may affect control strategies. Control programs for S. mansoni center on repeated rounds of chemotherapy every 2-3 years to reduce infection intensities and thereby reduce morbidity. Prevalence is much less affected and transmission is not interrupted, since these populations rapidly recover. The resultant effect of periodic contracting and re-expanding populations on schistosome biology is not known in large part due to the lack of tools and methodologies for differentiating subpopulations of worms. We have identified 7 polymorphic microsatellite markers that behave like single-copy loci, are species-specific, and produce interpretable patterns for DNA isolated from parasite eggs. Further, to optimize sampling, we have developed methods to isolate parasite egg DNA from stool and statistical methods that utilize allele frequencies from pooled samples rather than discrete genotypes. In order to understand how repeated chemotherapy changes S. mansoni population structure, this proposal will directly determine the allele frequency distribution of S. mansoni by isolating and genotyping egg DNA from the stool of infected individuals. These allele frequencies will then be related to the regional and microgeographic distribution of the parasite before and after yearly chemotherapy. With the tools we have developed, this project will: 1) Determine how microgeography relates to subpopulation distribution and gene flow, 2) Determine how widespread chemotherapy changes population structure, 3) Determine how populations that persist after chemotherapy are related to pre-treatment populations, 4) Measure the contribution of migration or increase in the resident population to recovery of schistosome populations, 5) Assess the contribution of local parasite transmission versus immigration to urban foci, 6) Compare urban foci to rural populations before and after therapy. Population structure will be compared using the between populations fixation index (Fsr) and by estimation of both effective population size (Ne) and the immigration rate (m). Mixed stock analysis will also be used to analyze migration.